Attic Ventilation Research Articles

Assessment of hygrothermal performance and mould growth risk in roofs of post-retrofitted non-dormer and dormer attic rooms with reduced ventilation

Building insulation upgrades focusing on energy conservation must also consider the hygrothermal performance of materials and the indoor environment. Previous research has shown that deep insulation retrofit may inadvertently reduce ventilation and increase relative humidity, increasing the risk of mould growth. This study used traditional housing in Ireland with pitched roofs as the case study to examine changes in the hygrothermal environment following the energy retrofit of a dormer-style attic room. The study compared the mould growth index (MGI) of roof rafters under different energy retrofit scenarios to understand the effect of adding a habitable dormer-style attic room on the house's mould growth risk. The results show that adding an occupied dormer room can increase the MGI of spruce rafters from below 1 to around 5.2 at 0.2 air changes per hour (ACH) of infiltration. In most scenarios, a ventilation rate lower than 1 ACH cannot prevent the MGI of rafters from reaching the critical threshold of 3, unless a 1 mm vapour barrier is added. A ventilation rate over 5 ACH is adequate to limit the mould growth risk, but mechanical ventilation may be required to achieve this level of attic ventilation. This study enhances understanding of the relationship between attic roof ventilation rate and the risk of mould growth during the energy upgrade of dormer style attic rooms, a common housing type across Northern Europe and further afield.

Presence and Function of Roof Ventilation in Housing Estates in the Humid Tropics

Traditional Indonesian and Dutch colonial buildings often include an attic for ventilation and natural lighting. However, most Manado homes have corrugated zinc roofs and no attic ventilation. Zinc-roofed building roof ventilation and thermal comfort in Griya Paniki Indah, Taman Mapanget Raya, and Kharisma Koka housings are studied. We created two test cells with and without roof ventilation. A vented ceiling cools the test cell by 1.2 °C during the day. Modern, simple homes with unventilated roofs dominate the three residential districts. All responders reported daytime and nighttime discomfort or excessive temperatures. Residents were striving hard to control the room's environment due to these conditions. Air conditioning, fans, windows, and ventilation are used daily. Thus, attic ventilation benefits must be publicised. This improves building and household energy efficiency and thermal comfort.

Openings in ventilated Attics

How big should ventilation openings be in ventilated attics? In Denmark, guidelines describe what is sufficient to remove excess moisture penetrating through the ceiling. These guidelines are based on many years of experience. An important parameter is the tightness of the ceiling. With current regulations for the airtightness of buildings, convection through the ceiling is reduced compared to older buildings. Therefore, it is relevant to review these old rules of thumb and maybe revise them. In this two-year study, tests with different sizes of ventilation openings were conducted in a test house with 18 separate ventilated attics and airtight ceilings. One third of the attics were ventilated according to the guidelines, one third’s ventilation was reduced by one third and the last third had 50 % ventilation of the recommendations. Hourly measurements of temperature and relative humidity in the attics were conducted. Rafters in the attics were tested for mould growth. Six different types of insulation systems were used in the attics (with and without a vapour barrier, different insulation materials, and insulation thickness), therefore, the study also includes these differences. Earlier investigations, with full ventilation in all attics, showed no significant hygrothermal differences between them; consequently, it was assumed that the amount of ventilation would be decisive for the hygrothermal performance. This study follows up on this assumption. Results show little differences between the attics, mainly that having a vapour barrier becomes more important with reduced ventilation, and the insulation thickness and thereby U-value is of less importance. Reducing the requirements for ventilation of attics could be relevant, provided that the ceiling is airtight.

Attic ventilation and radiant heat barriers in naturally ventilated galvanized metal-Roofed buildings

ABSTRACT The study's uniqueness stems from its goal of determining the efficacy of natural attic vents and radiation heat barriers on galvanized metal roof buildings in lowering attic and indoor air temperatures for thermal comfort in a humid tropical climate, a topic that has received little attention in previous research. This was accomplished by utilizing three separate experimental situations using two tiny models of single-sloped zinc-roofed houses, each with varied attic ventilation openings and radiant heat barrier applications. The thermal conditions of the attic and occupant rooms in the ventilated test cell tended to be cooler than in the unventilated one in the first experiment, which compared a test cell with 20% ventilation apertures in the attic to another test cell without ventilation. The second experiment, which compared a test cell with 10% attic ventilation to another test cell (without attic ventilation) with radiant heat barrier application, found that the radiant heat barrier's effect on temperature reduction was generally better. The third experiment, which compared a test cell with 20% attic ventilation to a test cell without attic ventilation but with radiant heat barrier application, revealed that attic ventilation outperformed the radiant heat barrier in terms of temperature reduction.

Influences on the drying behavior of a concrete ceiling below a cold attic

The article describes the current state of a project examining the influences on the moisture distribution in cold attics above concrete ceilings of residential buildings. Considerable research has been done on moisture damages in cold attics, especially in Scandinavia and North America, focussing on spaces above wooden ceilings. The project (ongoing until Sept 2021) underlying the article deals with cold attics above concrete ceilings resting on masonry walls, a frequent variant in Austria. Research was triggered by a regional Austrian building industry association to shed light onto recent detrimental moisture accumulation in the wooden wall plate (= bearing for the rafters along the eaves) and in the two EPS insulation layers on top of the ceiling. Suspected reasons for the moisture problems and for the local moisture distribution are 1) a too small diffusion resistance of the vapour retarder covering the ceiling, 2) insufficient (natural) attic ventilation and 3) convection, e. g. in the gap between the polystyrene blocks. In order to rank these potential causes by influence and also to find a practical solution a two stage experimental approach was chosen: 1) A handy small scale replica (order of dimension: 1m) of the situation was exposed to the according indoor and outdoor climate in a climate chamber. Different vapour retarders on top of the ceiling were chosen. 2) A larger 1:1 replica has been erected as well but not yet delivered monitoring data. In parallel, a hygrothermic model taking convection into account was established and simulations carried out. The project will deliver a contribution to the Austrian standard on moisture safety 8110-2 on how to judge the moisture safety of joints via simulation.

Aeration of the Human Prussak's Space: A 3D Synchrotron Imaging Study.

Prussak's space (PS) is an intricate middle ear region which may play an essential role in the development of middle ear disease. The three-dimensional (3D) anatomy of the human PS and its drainage routes remain relatively unknown. Earlier studies have histologically analyzed PS, by micro-dissection and endoscopy. Here, we used synchrotron-radiation phase-contrast imaging (SR-PCI), 3D reconstructions, and modeling to study the framework of the human PS, including aeration pathways. It may lead to increased understanding of development of middle ear pathology. Nine human temporal bone specimens underwent in-line SR-PCI at the Canadian Light Source in Saskatoon, Saskatchewan, Canada. Data were processed with volume-rendering software to create 3D reconstructions using scalar opacity mapping and segmentations to visualize its walls in fixed, undecalcified human temporal bones. The PS was found to be an irregular, variably shaped chamber with different aeration systems. Three different drainage pathways were found: 1) via the posterior malleolar pouch of von Tröltsch in seven of nine ears; 2) directly posterior-inferior into the mesotympanum medial to the posterior malleolar pouch in one ear; and 3) anteriorly in another. The posterior-inferior communications depended on the anatomy of the posterior malleolar fold. In one bilateral case, the aeration differed between the ears. Earlier descriptions of upper ventilation routes between the PS and the epitympanic spaces could not be substantiated. The 3D anatomy of the membrane folds organizing the PS in humans was demonstrated for the first time using in-line SR-PCI. The PS was always aerated into the mesotympanum, suggesting its relative independence of attic ventilation. The impact of its various drainage routes on middle ear ventilation and disease were discussed.

Moisture-safe attic design in extremely cold climate: Hygrothermal simulations

Attic ventilation is a commonly used method for the removal of moisture build-up in attics through air leakage from indoors, which is generally applied to cold climates. Un-ventilated attic is a fully sealed construction, which can prevent wind-driven rain penetration or snow accumulation. However, it does not provide an effective path for moisture removal, which may cause moisture-related issues. Northern Canada suffers from extremely cold conditions and very fine snow particles caused by extremely low temperature have high chances of penetrating into attics through vents or un-intentional openings during periods of high winds. To provide adequate attic design recommendations for this climate, hygrothermal models of ventilated and un-ventilated attics were firstly validated by comparing with field measurements and then used for a parametric study. The attic ventilation rate, ceiling air leakage rate and un-intentional air infiltration rate are set as variables for the parametric study to evaluate their effect on the hygrothermal performance of attics. Mold growth index (MGI) on sheathing is used as the performance indicator. For the ventilated attic, there is no mold growth risk, while for the un-ventilated attic, the MGI increases with the increase of ceiling air leakage rates and the decrease of un-intentional air infiltration rates. North-facing roof sheathing has higher MGI compared to south-facing sheathing. The parametric study results show that attic ventilation is required for the extremely cold climate and an un-ventilated attic has greater risks of moisture problems unless the ceiling air leakage from indoors is well controlled.

Hygrothermal conditions in ventilated attics with different air change rates and ceiling constructions

A recently Danish study reported that no vapour barrier is needed in ceilings, if the attic is well ventilated and the ceiling towards the dwelling is airtight. Based on that study, new investigations were initiated with focus on the hygrothermal behaviour in ventilated attics with different air change rates. A test house with three sets of four different ceiling constructions – all airtight – was used in this study. The ventilation rate was reduced in two of the sets with approx. 35 % and 50 %, respectively. Air change rates were measured with tracer gas. Furthermore, temperature and relative humidity was measured every hour. Measurements in similar ceilings with mineral wool or cellulose-based insulation material show that hygroscopic properties of the insulation have very limited effect on relative humidity. Furthermore, only at low ventilation rate the effect of a vapour barrier could be measured with minor impact. Based on the short-measured period the calculations of the risk of mould growth showed no risk. The results indicate that even when the ventilation is reduced by 50 %, the ventilated attic still performs well if the ceiling is highly airtight. However, the importance of vapour barriers becomes more important at lower air change rates.

Roof-integrated radiative air-cooling system to achieve cooler attic for building energy saving

The building attic usually subjects to substantial solar heat gain and has much higher temperature compared to the conditioned living space during the day, especially in summer and in hot areas. Reducing attic temperature can reduce cooling energy consumption in buildings. However, conventional techniques such as cool roof or attic ventilation, suffer from either heating penalty in winter or limited attic temperature reduction. In this work, a new roof-integrated radiative air-cooling system is introduced, which couples radiative sky cooling with attic ventilation to reduce attic temperature. A radiative air cooler with 1.08 m2 surface area is constructed using a recently developed daytime radiative sky cooling metamaterial [Zhai et al., Science 355, pp. 1062–1066, 2017]. Experimental tests show that sub-ambient air cooling is achieved throughout 24-h day-and-night cycle in a summer day with clear sky conditions. Depending on air flow rates, measured sub-ambient temperature reductions of air are 5–8 °C at night and 3–5 °C at noon under direct sunlight, respectively. An in-house model is first developed for the radiative air-cooling system, the model is then coupled with EnergyPlus to study annual energy saving of buildings. The performance of the radiative air-cooling system is compared with three reference systems: shingle roof, attic ventilation, and cool roof. Results show that for a single-family house, attic temperature can be substantially reduced by 15.5–21.0 °C, varying with attic insulation level, compared to shingle roof on typical summer days. Compared to a shingle roof (solar reflectance 0.25, thermal emittance 0.9) residential building with attic insulations of R-30 (RSI-5.28), R-10 (RSI-1.76), and R-0.8 (RSI-0.14), the roof-integrated radiative air-cooling system can achieve annual cooling energy savings of 0.4–1.5 kWh/m2 (4.6–18.8%), 1.2–3.6 kWh/m2 (10.2–41.4%), and 3.7–11.8 kWh/m2 (26.5–76.1%) respectively.

Hygrothermal performance of cold ventilated attics above different horizontal ceiling constructions – Field survey

To save energy ceilings towards a ventilated cold attic space are normally insulated. In Denmark the insulation material thickness and type varies but the common used insulation material type is mineral wool or cellulose-based insulation. Furthermore, some attics have vapour barriers, whereas others do not or only have poorly sealed vapour barriers. The effect of these variations on the humidity conditions in cold ventilated attics was investigated in preparation for evaluating the existing recommendations on when and how to add additional insulation to ventilated attics to reduce energy consumption. The investigation has been done by examining and measuring the relative humidity and temperature for at least one year in 34 attics in inhabited single-family houses. In addition, outdoor and indoor temperatures and relative humidity were measured. The results were divided into different groups based on the vapour barrier type, amount of insulation, and insulation material type. Most of the attics were ventilated according to the Danish recommendations. Contrary to the expectations, the thickness of insulation material had no effect on the temperature or relative humidity in the attic. The type of insulation material or the presence of a vapour barrier also did not have any noticeable effect. Apparently, the air change rate (ACH) is more important than the investigated parameters. Combined with previously published results from controlled full-scale experiments, the results from this study are valuable input to new recommendations on how to apply additional insulation in existing ventilated attics.

Why Is the Attic Ventilation Disappearing from the Current Urban Houses in the Humid Tropics?

The construction of a townhouse built today no longer has roof vents, compared to colonial buildings as well as traditional architecture scattered in humid tropics. In Indonesia, many buildings are made with a zinc roof, even in North Sulawesi province 92 percent of zinc roofed buildings or metal aluminum. This article has two purposes, the first is to assess the benefits of attic ventilation, especially for zinc roofed buildings and the second is to find out why the ventilation loft is no longer used to present buildings. Research by building two same test cells where one cell has roof vents, and the other cell does not. The test cell with ventilated roofs has the advantage that the interior temperatures are lower on average by 1.2 ∘C than those in a cell without ventilation. Almost all buildings today have a modern and minimalist style where the shape and pattern are delicate and do not allow for roof ventilation; such structures cannot form adequate attic spaces. Based on observation and evaluation, this is the leading cause of the disappearing of attic ventilation.
 Another thing was caused by efforts to reduce the selling price of a house with consideration of people’s purchasing power. Ignorance from building owners and developers on the benefits of attic ventilation to reduce room temperature and lighting is one of the factors found in this study; even this problem is made worse by architects who often ignore these benefits in their designs. Comprehensive knowledge is needed for the general public and also for architects for the use of roof ventilation which in turn is an effort to achieve thermal comfort and energy savings in the domestic sector

Must attic ventilation be preserved in energy retrofits?

PurposeThe addition of thermal insulation into attics along with air-tightening of the ceiling plane is a common first step in making homes more energy efficient. Attic ventilation was introduced decades ago on the assumption that air leakage across the ceiling was inevitable and not correctible – this was before the era of spray-applied foams. Often attic ventilation is provided at roof eaves, and ensuring good insulation in their location is critical to avoid cold corners in the rooms below. So may vents be blocked in the course of energy retrofits? The paper aims to discuss this issue.Design/methodology/approachThis study consists of a simple spreadsheet model of attic performance. The model is built using material from ASHRAE Handbook Fundamentals and ASHRAE Standards. It includes: Glaser calculations for temperature, vapor pressure and vapor pressure excess; radiation exchange – solar and sky; buoyancy flow assumption for leakage from indoors; wind flow assumption for leakage from outdoors; and change in attic air RH as assumed indicator of change in sheathing moisture performance.FindingsThe model results show that lowered moisture contributions across air-tightened ceilings may compensate effectively for added insulation (which lowers the attic air temperature) and reduced moisture dilution from attic ventilation.Originality/valueThese results provide support for the policy of allowing attic ventilation reductions that are proportionate to ceiling air leakage reductions as part of weatherization efforts. Given the limitations of the model, continued field observations remain critical.

Field measurements of hygrothermal performance of attics in extreme cold climates

Attic ventilation is typically recommended for the removal of moisture build-up caused by air leakage from indoors in cold climates, however, it may also increase the amount of snow and rain penetration into the attic, especially in the extremely cold climates. In northern regions, extremely cold temperatures can cause snow particles to become very fine, which will penetrate vents or unsealed openings. The snow accumulated in the attic would melt at temperatures above zero and penetrate to indoors through the ceiling and cause moisture problems. One of the solutions is to add filter membranes along a ventilation cavity behind the façade to prevent snow from entering the attic. The ventilated attics with filter membrane had some success but there were instances with reported water leakages and moisture damages. There have been also attempts to use un-ventilated cold roofs. Un-ventilated attics prevent snow accumulation but do not allow for effective removal of moisture, which could be risky and prone to moisture damages.This paper presents a field study of the hygrothermal performance of three attic venting systems. Three houses with different attic designs built in Canadian North were monitored: two with a ventilated attic but different strategies controlling snow entry and one with an un-ventilated attic. Measurements show that the ventilated attics had acceptable conditions. The moisture content of wood structure at most monitored locations in the un-ventilated attic remained above 20% through the summer, which indicates that without ventilation the construction moisture and moisture accumulated through winter cannot be effectively removed.

Ventilation of Low Slope Roof Systems in Northern Climates

For over generations, multi residential (flats) buildings were constructed in North American with low slope roofs. The roof design included an interstial space of 1.5 to 2 meters between the ceiling and roof deck. This ‘attic’ space was typically vented via static air vents. The ceilings were typically constructed of plaster with little or no insulation. The roofing was typically asphalt or coal tar built up roofing applied directly to the roof deck. This simple ceiling to roof arrangement worked for centuries. In circa 1998, with the advent of mandated reflective roofs in several large North American cities, a simply workable design was changed, often with disastrous results. So that greater floor to ceiling heights could be attained, the 1.5 to 2 meter attic was reduced to .33 m or smaller. Plaster ceilings were changed to gypsum board. Fiberglass insulation with an ineffectual vapor barrier was installed at the ceiling, and often punctured by ‘can’ lights which allowed air transport of warm air, often containing moisture, into the attic cavity. With no attic ventilation, insulation on the roof deck, condensation accumulation on the attic structural elements to such a degree that, in many situations, resulted in the deterioration of the wood structural elements.This paper will review the importance of proper design with ‘modern day’ low slope roof systems with ceilings on the roof structure, and the role that venting, vapor retarders and roof color have on the success or failure of these roof systems. The author will review historical examples of recent failures and provide designers with recommendations for appropriate low slope residential roof system design.

Mrmc Neo Surgical Ventilating Port and Neo Attic Malleo-Incudal Complex in Endoscopic Management of Limited Attico-Antral Cholesteatoma.

To study functional outcome of the endoscopic management of limited attico-antral cholesteatoma in terms of visualization of sac, cholesteatoma disease clearance, ABG closure improvement, preservation of residual anatomy and recurrence of disease. It is a prospective study done during Feb 2016 to March 2017 done on 20 pts with limited attico-antral cholesteatoma with CT confirmation. Endoscopic management of limited attico-antral cholesteatoma with complete removal of sac, infected discharge and granulations along with creation of MRMC Neo surgical ventilating port (joining Anterior & posterior isthmuses) done in cases where residual attic anatomy was present to establish physiological attic ventilation and drainage. Whereas in cases of attic and ossicular erosion, ossiculoplasty along with neo attic malleo-incudal complex (with composite tragal cartilage with perichondrium graft) for lateral attic wall reconstruction was done to prevent attic retraction. Patients had mean pre op ABG of 36.29±6.29 and mean post op ABG closure of 16.33±6.50 with no recurrence of cholesteatoma at 6months of follow up. Patient showed significant (55%) improvement in hearing with all having graft uptake in which four cases having mild pars tensa retraction which recovered later without any intervention. Thus creation of new MRMC Neo surgical ventilating port or neo attic malleo-incudal complex with endoscopic approach allows better visual access to clear the limited attico-antral disease with sparing of normal residual attic anatomy along with physiological ventilation and drainage having better hearing results and outcome.

Bats of the city of Banská Bystrica, Central Slovakia (Chiroptera)

Abstract Based on published findings (1900–2010), unpublished data from museum specimens (1965–1999) and data from recent field survey (2006–2013), the presence of altogether 15 bats species was recorded from the urban area of Banská Bystrica in Central Slovakia. Nyctalus noctula, Vespertilio murinus, Pipistrellus pipistrellus, Eptesicus serotinus and Myotis daubentonii were found as common species in the area. Nyctalus noctula was a predominant species (D=67.4), followed by Vespertilio murinus (D=15.2) and Pipistrellus pipistrellus (D=9.8). The systems of concrete blocks of flats (attic ventilation holes, dilatation fissures, various systems of plumbing accessories, damages of buildings, etc.) represent the most important features of the artificial urban habitat for bats. Most frequently, the hibernation aggregations found in the buildings were formed by Nyctalus noctula, Vespertilio murinus and Pipistrellus pipistrellus, while the occurrence of Myotis myotis, M. mystacinus and M. emargiantus was only occasional. No maternity roost of bats was recorded in the city of Banská Bystrica.

Residential energy retrofits in a cooling climate

In this analysis we calculate the effect of energy retrofits in almost 500 homes in Austin, TX. We used measured daily energy use data (kWh/day) from before and after the homes received energy retrofits. These retrofits included attic insulation, new heating, ventilation, and air-conditioning (HVAC) systems, window screen/film, new windows, new ducts, and added duct insulation. We used a mixed effects regression model (with and without interaction terms) to identify the impact of each type of retrofit, as many homes received multiple measures. We used both utility rebates (to the homeowner) and total retrofit cost information to find the levelized avoided cost ($/kWh) of energy consumption to both the rebate issuing entity (in this case, Austin Energy – the local municipally owned electric utility) and the homeowner. Results indicate that, at current rebate levels, all “rebate costs” incurred by the utility are less than the average cost to procure energy on the wholesale market ($0.035/kWh). Thus the utility could make a profit by forgoing energy sales to local residential customers and instead selling into the market. Regression results show that increasing attic insulation, replacing older heating, ventilation, and air-conditioning (HVAC) systems, and replacing duct systems will most likely be cost effective for the homeowner at the current time, i.e. the costs are less than the current electricity rate (about $0.11/kWh), but replacing windows might not.

Drying Potential of Cold Attic Using Natural and Controlled Ventilation in Different Swedish Climates

Problems with high humidity levels and mold growth in cold attics have been increasing over the last few years. The high humidity levels are to a large extent a consequence of the increasing demand on energy efficiency. Houses are frequently retrofitted with additional attic insulation, which leads to a colder attic space and hence a higher humidity. Replacing furnace heating by heat pumps or district heat may also lead to problem. Also newly built attics have problems. The quite novel technical solution with controlled mechanical ventilation of the attic is generally estimated to be risk free in Swedish climate. With controlled mechanical ventilation the attic is intentionally ventilated only when the inflowing air is drying out the attic, otherwise it is shut off. The drying potential of controlled ventilation is analyzed for different climate zone in order to map the relative efficiency compared with traditional natural ventilated attics.

Effect of Attic Insulation Thickness and Solar Gain in a Mild Climate

Attic air ventilation can be influenced by various vent considerations. In addition to vent ratio and location of roof vents, attic insulation thickness can be considered as an influential factor in attic air flow and temperature distribution. Most existing building codes do have a minimum requirement for venting parameters and type and thickness of the insulation used. In this paper, the effect of insulation thickness in attic ventilation rate, attic air temperature and heating and cooling loads in a mild climatic zone is studied. A typical mild climate summer and winter temperatures and solar radiations data are used for 24 hours transient conjugate heat transfer simulations. Results show that solar radiation has significant impact on the amount and the pattern of airflow in attic. An increase in attic insulation yields a decrease in attic ventilation during winter period, but has no effect in summer period for the climate considered. In general, the higher the attic insulation thickness is the lower the building takes advantage of solar gain during winter period, but higher insulation levels tend to be advantageous during summer cooling period.

A Computation of U-Factor for an Entire Vented Attic Assembly using a 2D Model

The overall U-factor values for an attic assembly are usually computed with the ANSI/ASHRAE/IES based R-value (thermal resistance) conversion. In the ANSI/ASHRAE/IES Standard 90.1 (2010), the effects of attic air resistance, roof pitch and attic width are not taken into account while calculating the U-Factor values. In addition, the R-value is estimated using a one dimensional thermal resistance model. In ventilated attics, where the insulation near the roof sheathing is tapered, it is difficult to find the correct R-value of the attic system as the heat transfer becomes two dimensional. In this paper, a 2-dimensional CFD model is developed for various insulation R-values and insulation taper angles near roof decks. COMSOL Multiphysics 4.4 is used to model and analyse the attic structure. Results show that a discrepancy in overall U-factor for entire attic assembly between the developed model and the existing standard estimation. These results are pronounced for lower slope roofs with high insulation thickness.