My Mother is the original owner of a basic, rectangular, 1,100 sq. ft bungalow, built in 1952 in Crescentwood. Each end of the roof peak extends to form a gable, bearing a wooden louvered face as part of the attic ventilation system. The louvers run the full width of the face of the gable and are constructed of 1×3 slats. The immediate problem is that this wood has now reached its limit and several of the slats are starting to rot and come loose.
From a functional perspective, this ventilation system has served the house very well over the years. In addition to these two gable vents, my parents had installed two pairs of soffit vents, one at each end of each long run of the house. These vents are metal units, the size of a typical cold air return register. In addition to the original four to five inches of wood shaving insulation in the attic, two layers of R20 fibreglass batts were added. The first was laid parallel with the ceiling joists and the second perpendicular to the first. Clearance was maintained over the soffit areas to allow adequate airflow. The attic access hatch was hinged, a rubber gasket added around the edge and the wooden hatch insulated. The only two long-term maintenance issues they have ever experienced have been snow blown in after large blizzards and wasps entering between the wooden slats, setting up home in the attic.
Taking all of this into consideration, I can identify three possible routes to take for repairs. Firstly, I could have the gable vents replaced with identical new assemblies with custom carpentry work, which would not eliminate the two previous problems. Secondly, I could replace the entire vent areas with painted plywood and install new style plastic or metal pre-made screened vents. This may adversely reduce attic airflow, due to the smaller vents. The final option is to complete option two and also add an appropriate number of the new square style attic vents that fit on the upper roof surface. This route currently has the most appeal to me.
I do wonder, however, if it would create any problems in the wintertime, when it is not unusual for these types of vents to be buried under heavy snow for weeks or months on end. I am assuming that if the attic is properly sealed, this is likely not a serious concern. Any insight or other possibilities you can suggest would be greatly appreciated.
I chose this question to end the Sunday Homes series of Ask the Inspector because attic ventilation and air sealing has been a favourite topic of mine over the years. I will offer a relatively simple answer to your excellently thought out and articulated question.
If I were the owner of the home in question, I would opt for your third choice for two simple reasons. It will likely be the most economical and easy solution while improving the already reasonable attic ventilation. Having said this, I might opt for the first proposal if aesthetics are a major concern. You may want to have the original vents rebuilt to maintain the original look of the home. If this is your choice, simple installation of aluminum screening on the attic side of the vent should eliminate the insect problem and may help a little to stop blown-in snow.
I prefer the third option not only because of the economic reasons, but also the roof vent component. One or two simple roof vents placed near the centre of the roof, as high up as possible, will help prevent condensation in the areas furthest from the gable vents. This is the location in older attics that typically traps warm air escaping through the ceilings and forms frost when the weather drops well below freezing. Placing the new vents near the peak will minimize the snow cover, and the warm air escaping these vents should melt snow over the vented areas under the cap, allowing proper airflow. Your concern for the reduction in surface area for ventilation with the smaller gable vents may be easily accommodated with the new roof vents. In addition to this, you could easily cut in two or more soffit vents nearer the centre of the house to improve attic ventilation even more. Either way, you should still be within the suggested ratio of attic venting to square footage of ceiling space.
To follow up on this last point, it is recommended to maintain a ratio of between approximately 1:300 and 1:400 for attic vents to ceiling square footage. To simplify, you should install one foot of venting for every 300 to 400 square feet of attic floor, in a well-insulated attic like yours. What is not addressed in many recommendations is that this ventilation should be distributed as evenly as possible throughout the attic with different vents. For this reason, the addition of roof vents and additional soffit vents should more than compensate the reduction in size of the older gable vents. This will improve the distribution of ventilation that was previously concentrated only high up at the gable ends.
For those loyal readers wondering about my opening statement, Ask the Inspector is not coming to an end, but simply shifting its time and location to Thursday. Accompanying this change, the focus of the column will be altered to address concerns more specifically related to buying and selling homes. I encourage everyone to send in new questions related to this new angle and anything else related to the role of Home Inspectors in the entire Real Estate process. I would like to gratefully thank all those who sent in an inquiry over the last six years and made the column a success. I am constantly surprised and encouraged by the level of knowledge of the respondents. See you all on Thursdays.