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Question DetailsAsked on 5/31/2016

Should I install ridge vents? I have flat roof (<2:12 pitch), torchdown on plywood, rafters, then drywall. Too hot.

I plan to reroof soon, as I currently have 20+ year old hot mop / rocks. I expect the torch-down is best option due to low pitch. I am looking into how I can cool the house in hot months (San Diego), including ridge vents, ACFoam-II, and adjustable (venting) skylights. Appreciate any suggestions / advice. Thanks.

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5 Answers

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Since you are in a no-snow area and don't have to worry about ice damming, and not an area with common driving rain or tornadoes or hurricanes, I would go with ridge vents at a minimum - making sure they are the raised type designed for low-slope roofs.


Another thing you can do to reduce heat - go with low heat absorption roofing - white or light gray synthetic membrane roofing or heat-reflective aggregate on a torch-down built-up roof, and of course yoiu can use foam roof insulation under the membrane (be it synthetic or built-up type).


At that sloipe definitely a membrane versus shingle roofing situation, though raised-seam metal sheet roofing could also work if you desired - though of course while more maintenance free and much longer lived, you pay a higher initial cost for those benefits so the out-of-pocket impact turns some people away even though in the long run you generally save money (if you stay in the house indefinitely). If you went with metal roofing, you could go with insulation under it and/or a "double-layer" roof, where there is ventilation under the metal roofing to remove much of the heat, exiting through a ridge vent.


Venting skylights I generally advise against just because people fail to close them or are away from the house before it rains, though not so much a consideration in your area - though depending on where in the area you live blowing sand or dust might be.

Answered 2 years ago by LCD

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Thank-you much LCD. I really appreciate your inputs. I hadn't considered the dust.

Answered 2 years ago by CRBerger

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Yeah - if in a dust-rich environment (desert, beach, glacial outwash area, tilled/plowed farm country) then venting skylights can be a problem. There is at least one brand, it has been years so I don't remember the name, which has a tilting interior frame at its base, which can be moved up and down manually with a reach pole or motorized for high ceilings - the tilting panel can be closed to close off ventilation, or opened to allow airflow in under the fixed panel skylight. They made a replaceable filter pad element to fit into that panel area to filter out dust - saw it used on an aircraft hanger in Nevada desert where they did aircraft maintenance which was sensitive to dust. Problem with the filter elements is they had to be on the inside behind rainguard louvers so they would not get wet, which meant having to be able to get to them to change them out. Not a problem in the hanger case because there was a catwalk under the skylights to allow cleaning and also ceiling-mount lightbulb changing - but in a house you would have to be able to get up there to change the filters. Also - not something that would be good if there is any potential for ice damming or snow buildup that could leak in through the vents. In that sort of case, probably better to use fixed skylights and separate ventilation means.


In your case - unless you are out in the inland Rancho area or right along the beach or maybe near a sandy area like Camp Pendelton or Miramar NAS, blowing sand/dust is probably not a major issue.

Answered 2 years ago by LCD

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Thanks again LCD! Your inputs are greatly appreciated. Just to be sure, ridge vents are a good idea even if I don't have an attic? I underestand they would allow ariflow through the space between the rafters, assuming there is nothing in there to block the flow, which I expect is the case. Once again, your detailed aswers are awesome!

Answered 2 years ago by CRBerger

1
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Unless your rafter bays have been totally filled with insulation (which is a bad idea anyway), as long as you have about a half inch or more of airspace above the insulation for airflow, the ridge venting should be a good idea, even with the low-slope roof for your area where heavy wind-blown rain and snow/icing are not a concern. You should be able (if you are able to get up on a ladder) to see up into the eaves (unless soffit covered) with a strong flashlight to see if there is an airspace above the insulation - or in your locale there may be no insulation at all and just open rafter bays, which is even better.


Be sure the contractor proposes a ridge vent designed for low slope roofs - has a higher wind/splash barrier at the bottom edge to prevent splash/windblown rain from driving in along the shingles into the vent - cost very little difference from normal vent but less likely to leak in a blowing rainstorm.


Note if ridge vents are put in, any gable (endwall) vents should be blocked off in areas served by the ridge vents to prevent short circuiting - though you would normally not have gable vents if you have just a cathedral ceiling with rafters asd opposed to trusses or an attic.

Answered 2 years ago by LCD




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