Trained Eye

 
 
 

Adding Sunroom

Question:

We are looking into attaching a three-season sunroom to an eastern exposure on our home. The dimensions are approx. 25' x 14'. We are most likely going with the glass & vinyl sides with a prefab roof, not a traditional shingle roof. This roof will slope away from the facia. Our house set up is an L-shaped roofline.

Here is the question related to attaching the unit to the house.

We expect the sunroom to get quite warm as it is an eastern exposure and sitting on the existing deck can get unbearable. One company indicated it would attach the sunroom roof to the fascia, while the other said it would tie right into the existing roof rafters, eliminating the soffit and fascia. The latter stated the soffit would be blocked off since it was not their recommendation to vent the heat from the sunroom up into the attic. They don't want to overheat the attic. Since there are plenty of roof vents and the soffit is continuous around the house does this make sense? My thought is that it would be better to vent the heat rather than keep it contained in the sunroom.

You advice would be appreciated.

Answer:

Adding on unheated sunrooms is becoming a very popular choice for many homeowners to extend the use of their patio or deck beyond the summer months. It also will help prevent the recent crop of mosquitoes from making back yard use difficult. You have asked an excellent question, and I commend you on your request for more information on this topic. Although the sunroom is not heated, it is still added living space to an existing home, which can cause unforeseen problems if not taken into account during construction.

There will indeed be some additional heat build-up in the sunroom, due to passive solar energy coming in the large windows. Having a manufactured roof will limit the amount of heat compared to a tempered glass roof or even a dark coloured asphalt roof. The eastern exposure may not be that troublesome, as the sun will mostly enter during the morning, unless it has southern exposure as well. I would suspect that this overheating would be most noticeable in the hot summer months, which could be minimized by leaving the windows open as much as possible. Any heat that would enter the attic at that time of year would not normally be troublesome as long as adequate ventilation was in place on the roof.

Attic ventilation is important in the summer, to allow heat to escaped that may build up inside from the sun’s rays hitting the roofing, but is much more of a concern in the heating season. Adding the sunroom to the exterior of the home will not normally create enough added heat in the winter to cause condensation in the attic, if the first construction plan is followed. It may be a problem, though, in limiting the fresh cool air entering the attic from the original soffit vents. If the windows are closed for the winter and relatively well sealed in the sunroom, cool fresh air may not be adequate for the soffit vents. This, not heat, may actually be the concern of the second contractor. A simple solution to this would be to leave some of the windows slightly open in the winter to allow cold, fresh air to enter the new, unheated space and prevent this problem.

Eliminating the soffit vents, in the second scenario, will simply reduce the amount of fresh air taken into the attic and may be more troublesome than the other method of installation. If the second method is chosen, additional soffit vents should be installed as close as possible to the area that they are removed. Depending on the design, the addition of these new vents or more roof vents in that area may eliminate any problems.

The choice of the sunroom roof attachment to the house may have a moderate issue with relation to attic ventilation, but may have a much larger concern with relation to snow build-up and possible leakage. Changing the pitch of an existing roof, by adding an addition, is often a problematic situation in relation to snow build-up and water runoff. If the existing home has a fairly steep pitch, on the East side where the sunroom is to be added, it will change dramatically on the new structure. Transitions from a steep roof to a much lower pitched one often cause a problem with snow accumulation, ice damming, and possible leaks. This is especially the case with most sunrooms, which have a single pitched, shed-style roof. Care should be taken to choose the design that most closely follows the original pitch of the house. In this case the second scenario, with removing the existing soffit, will make the sunroom roof higher and will likely match the existing pitch more closely. This may also allow better installation of a metal flashing between the two roofs, to prevent leaks. It may also allow easier clearing of heavy snow loads, which is highly recommended for low-slope roofs.

This should be your real concern about the sunroom roof design and you should inquire with the contractors about their solutions to this possible problem. Also, ask for references and talk to homeowners who currently have a similar set-up to your proposed addition, to see if they have had any problems.

 

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