From Engineering on October 17, 2008 in Air Conditioning & Heating
Recently we received the following comment:
“Last summer I purchased an old one-and-a-half story house, probably constructed in the 20s, 30s, or 40s. The second floor (1/2 story) just has two small bedrooms and a shared closet. The roof is a 4-sided hip roof with three dormers. The upstairs is excruciatingly hot in the summer and, in spring and fall, it is still way hotter than the downstairs. I live in Atlantic Canada and this heat is unusual for me. Inside the eaves (behind the knee walls), it is even hotter. It appears to me that the enclosed eaves and ceiling of the 2nd floor have no ventilation and so the heat just builds up all day. From what I can tell, the soffits are boarded shut. So, the only ventilation is from the 3 small dormer windows, but it just will not cool off at all. It is so hot that no one can sleep up there. Do you think my assessment of the cause of this problem is correct and, if so, can I fix it? Is there some technique or product that I can use to ventilate the eaves to the outdoors? Someone suggested a cupola or a ridge vent for the attic/peak, but Im not sure what to do about the eaves. Your thoughts would be appreciated. Thanks.”
I would guess your assessment of the problem is spot on. It sounds like there is zero ventilation in the attic and soffits and, therefore, nowhere for rising warm air to go. This is not only uncomfortable but bad for the building materials up there. Thankfully, there are plenty of solutions for providing air flow through the attic.
As for the roof, yes ridge venting is a good idea. However, considering that your roof is a four-sided hip design, Im not sure how much ridge you have to work with. I will say that ridge venting is typically the best way to vent a roof because it does not allow any warm air to be trapped in the upper reaches of the attic. Another option would be to cut vent holes in the roof, usually a few feet down from the peak, and install vents. You can even install vents with built-in fans to encourage airflow, should you so choose. You do live in Atlantic Canada where excessive heat is not a typical problem, so I think allowing air flow should be enough.
Now to the soffits/eaves. It is vital that air be allowed to flow in and out of the attic. So venting the roof is one part of the problem. Allowing fresh air to circulate through the home is another. Venting the soffit is as easy as cutting rectangular holes (roughly 2-3"x 14”) every six to eight feet along the soffit runs. You can buy standard soffit vents from any home improvement store and just screw them into the soffit boards.
You may run into the obstacle of continuous roll blocking between the trusses where they sit on the exterior walls. If no avenue for air flow was allowed when the house was built then you have a bigger problem. You may need to either remove at least some of the soffit or climb up into the attic however you can gain access to this area. Then youll need to drill holes through roughly every third block to facilitate ventilation. Then reinstall the soffit complete with vents.
In the same way you complete an electrical circuit, you need to create a circuit for air to flow through the home. Also think about insulation, if its lacking, to protect against heat gain and loss. This is all fairly simple but laborious and probably dangerous work. Therefore I highly recommend hiring a professional contractor to do the work. He or she will also be able to assess the situation on site in a more specific way. Remember, it usually doesnt cost anything to get a professional opinion and you can go on from there. Hope this helps!