Our photo at page top shows a modern synthetic mesh type ridge vent (with modest airflow capacity) and our photo at left shows a typical installation of continuous soffit or eaves intake venting at the lower roof edges of a building.
Problems With Roofs Lacking Any Overhang - No Soffit?
Don't give up on providing roof intake ventilation openings just because your building was constructed with no roof overhangs. In fact, providing exit venting (at a roof ridge or at gable end vents) on a building with no intake venting at the building eaves will increase the building heating costs and can also add to attic or under-roof condensation, moisture, and mold problems.
buildings such as the cape Cod shown at page top may be constructed with no roof overhang whatsoever. While this design offers the advantage of more light entry at the building windows (not shaded by a soffit), owners of buildings built with this design need to watch out for several problems:
Ice dam formation is likely in freezing climates if there is no under-roof ventilation. Ice dam leaks on any building but particularly buildings with no roof overhang increase the chances of water passage on or even inside the building wall, inviting mold, rot, insect damage, and wet insulation.
Gutter overflow leaks, should they occur, will send water running down the building wall, inviting the same problems just listed above, even in climates where freezing and ice dams do not occur.
Increased building heating or cooling cost will occur in heating climates if roof exit venting is provided with no eaves or intake venting. That's because warm air leaks and heat lost into the attic or roof cavity will create a building up-draft of air movement that, unsatisfied by a ready source of makeup or intake air from outside, will draw conditioned air out of the occupied building space instead.
Increased risk of attic or roof cavity condensation, mold, or insect damage will occur for the same reasons just described. In cool or cold weather, moisture laden air drawn into the attic or roof cavity will leave its moisture as condensation on the roof deck underside or in the attic or roof insulation.
Venting Solutions for Roofs with No Overhang or Soffit
Install special roof intake venting products that work at the lower edge of the roof decking, underneath the first course of shingles. Example: Smart Vent™, a special roof eaves vent product that provides a 3/4" opening about 6" above the top of the roof drip edge.
The Smart Vent is a tapered plastic vent product that is combined with a one-inch slot cut into the roof deck six inches from the lower edge of the roof. You will need to be sure that the air vent opening is not blocked by attic or under-roof insulation.
A similar product, the Hicks Starter Vent, patented by Massachusetts inventor Robert M. Hicks, is a combination of roof edge "starter vent" and drip edge. is cited at ROOF VENTING: Un-Vented Hot Roof Solutions. (We have had trouble finding this product).
Construct a hidden roof intake vent at the top of the building wall by removing the wall top trim or top siding board, cutting away any building sheathing or blocking at the wall top, nailing 1" spacer blocks 16" on center, nailing a new spaced-out wall top trim board along the roof eaves, and screening the opening against insects.
This design is used more often when there is an existing roof overhang but no soffit has been constructed to enclose the overhang.
If you follow this design on a building that has no roof overhang whatsoever, the gutter will need to be removed and re-hung on the new spaced-out fascia board or siding board, and you may need to extend the roof drip edge by 1 3/4" to assure that roof drainage enters the new spaced-out gutter. It should not be necessary, however, to actually extend the roof decking and rafter tails.
Our photo above shows a roof fascia vent at the eaves of a home in the Northeastern U.S. though in this case the builder also trimmed out a faux-soffit and fascia board (with no gutter yet installed). Our pen was stuck into the fascia vent opening to demonstrate it's width.
Construct a soffit, or eaves overhang, combined with assuring that an opening is provided all along the top of the building wall by removing any blocking between roof rafters at the top plate, combined with use of roof insulation baffles to assure an air inflow pathway under the roof deck.
Using this approach it may also be necessary to extend the roof deck out to cover the roof edge extension.
This is probably the most-costly solution to an un-vented no-overhang roof design, and is practical only in cases where the building is being modified for other reasons. On buildings where the top of windows are close to the top of the building wall, there may be insufficient space to construct an overhanging roof eave without blocking the windows.
Reader Question: do little air gaps in my DIY foamed roof deck built atop an existing roof lead to any issues?
2017/10/26 Bob said:
I have 1 room. Between garage and house. The roof is connected but independent. It has catherdial ceiling with fiberglass between the tounge and groove (interior) and roof sheathing. I want to make it a hot roof to prevent condensation.
I will tear off shingles at foamboard. Frame with 2×4s and spray foam cavitys and cover with plywood and re shingle.
I will be able to airtight the interior suppifficently. My concern is after spray foam and applying new plywood.
If there is small air gaps between foam and roof deck will that lead to any issues? Help is appreciated thanks.
[Click to enlarge any image]
Watch out: the roof design shown above is a sketch provided by the reader, is incomplete in that it does not show the details of the cathedral ceiling, and may require additional measures for fire safety and to meet building codes.
Reply: Possibly yes, both fire safety & design: a vented hot roof design may contain contradictions
I don't think foam gaps that do not communicate over any distance more than a few inches would be an issue as long as you are taking steps to be sure no indoor air/moisture leak into the enclosed roof cavity. You do that with a vapor barrier on the warm interior side and/or by using closed cell foam and taking care to seal around ceiling penetrations.
But I'm a bit worried about your design combining venting and multiple layers of roof structure that may be constructing a concealed space that is a fire concern.
To be accurate, I don't have a clear understanding of your structure. Be sure you're not building multiple layers of roof framing & sheathing in one roof - concealed spaces can be fire hazard and probably a code violation unless special fireproof measures are taken.
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roof venting in a mobile home
(June 17, 2014) Randy said:
I have a mobile home and the roof was metal with no sheathing. We removed the metal roof, round vent (about 8") and laid plywood down. The problem was there was no overhang or soffit/eave, so at the end of the Raffters we put a new 10" board. This board was at an angle, not straight plum like the wall just under it. This board's 1" width did get me beyonf the exterior wall's siding but as it tipped inward raising to the roof would but the drip edge too far inward so we placed a second 4"board at the top of the 10" board to give a shadow line and pus the drip edge outward one more inch. I then wrapped these boards in aluminum and put a small 1/4" bend outward at the bottom to help push the water away from the house's siding. Instead of replacing what was an entire roof vent that was 8in in diameter I ran a ridge vent to give the roof more ventalation. When the winter came water came in under my plumbing stack which was a new seal installed correctly with the roof.
I assumed that the issue was a lack of insulation in the area where the pipe passes throug the ceiling and the heat escaping was drawing in water. After doing a lot of reading here I am realizing that the ridge vent may be vacumming out the atmosphere from the attic (if you can say a mobile home has an attic). This may be why the water was sucked up under the stacks seal and drawn into the house, I can't remember if the 2 times I had water damage it was windy. I do know that heat loss can wick in water as well, even more so on a 3 or 4 pitch mobile home roof.
After reading this my plan is to tar under the stack seal and inastall gabel ends (maybe just one end) so the ridge vent has a source for air. The only insulation is on the ceiling so I do not think I need to undo everything I did at the ends of the rafters where a soffit should be since I do not need air movement between each rafter. What do you think? Does everything make sense?
Randy, take a close look at the water stains inside the roof structure to see where the leak is. If tte problem were interior moisture condensation you'd see those stains throughout the attic not just at the plumbing stack.
Question: repairing leaks at a plumbing vent stack
(July 14, 2014) Anonymous said:
The absolutely water came in through the stack, this could have been from an ice love (but the ice love was very small, an inch thick and the last row or two of shingles which is where the stack is).
My first communication was because I started thinking that the ridge vent is vacuuming out the air with no intake since I have no gabel end or sofit vents. The air intake may be at the underside of the stack and anywhere else air could leak into the roofs underside. I am trying to decide if I should cut a gabel end after sealing the underside of the stack seal. I cannot get back into the roof area, its all sealed off after we installed the new roof (including plywood that was not under the original metal roof) but there did not seem to be a water issue from moisture or condensation. The leak was bad and no doubt came from the stack and damaged the wall directly under. The low pitch roof and lack of sealant at the stack caused the leak but I wonder if I need an inlet to vent the roof properly since we installed a ridge vent. If I had huge ice damns then I would just say yes, but last winter was bad and I just had ice at the edge of the roof which is not an immidiate indicator there is a lack of air flow. Am I making sense?
I'm a bit unclear on "ice love" and "absolutey water"
(July 15, 2014) Anonymous said:
LOL....Sorry, the water absolutely came in through the stack. And I dont know what the heck happened but that should have read "ice dam".
When I say underside of the stack , I mean under the metal that is part of the seal around the vent pipe.
What I really want to know is should I cut a gabel end vent?
Leaks around a plumbing vent need to be fixed by properly flashing at that vent. Cutting other vent openings won't help.
Last spring I repaired a plumbing vent that had been broken off by sliding snow. I found a small amount of moisture in the roof cavity at the vent boot. I waited until dry weather, then left the vent opening at the roof open to the air during the day for several days to allow the cavity to dry. I closed and sealed the opening at night to prevent dew or a sudden rain from wetting the roof cavity.
When the roof cavity was dry I repaired the vent and flashing. You can see the details of this procedure at
Questions & answers or comments about attic moisture, condensation & ventilation: how to vent a roof with no overhang
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"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
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