FAQs about Hot roof designs, aka dense-packed insulated sloped roofs:

Here we answer reader questions about un-vented roof designs, hot roof designs, and specifications.

We discuss the durability of this design and include warnings about stumbling blocks to avoid.

This article series describes various solutions for un-vented cathedral ceilings and similar under-roof spaces, offering advice on how to avoid condensation, leaks, attic mold, & structural damage when roof venting is not possible.

Un-Vented Roof Problem Q&A

Questions & answers about designs for & problems in un-vented or "hot roof" designs originally given at HOT ROOF DESIGN PROBLEMS - you will enjoy reviewing the advice given there.

Photo at left: the author below a cathedral roof design that he constructed in the 1970's in New York. Using a labor-intensive but very aggressive under-roof ventilation design has seen this roof through over fifty years of subsequent use without ice dam leak issues.

Details of that structure are in the HOT ROOF DESIGNS article linked just above.

Why is there not one site on the internet that shows or tells how to properly vent an existing A-Frame style home?

Why is there not one site on the internet that shows or tells how to properly vent an existing A-Frame style home?

Many in my neighborhood (central WI) that were built back in the mid 80's to early 90's have no ventilation at all so moisture has no way to escape and rot begins to eat at rafters and decking.

I have images for your review to show the extent of hidden rot and decay.

Thanks - On 2016-10-25 by Di Haman

and from this reader

VENTILATION DILEMMA: Timber A frame style home. A frame roof goes from ground to peek, no soffit vents as the walls are one huge gable filled with insulation.

How can these A frame style homes be properly ventilated to avoid dry/wet rot or decay when there is no attic as the gable itself is living quarters?

Much appreciated if you have answers - On 2015-07-13 by Di

Reply by (mod) - A-Frame Roof Steps to Avoid Ice Dams & Venting Issues

Interesting question, Di.

I don't think you mean that the roof edges actually extend into ground contact - which would be a rather iffy roof design inviting rot and insect damage. So we hope that there's reasonable ground clearance.

Your options are to install a starter vent at the lower edge of the roof decking and a ridge vent at the roof top, or to go to a hot roof design.

If there is no actual roof cavity space thorugh which air could pass you're going to be looking at hot un-vented roof options.

I suspect the reason you don't see more about venting A-frame home roofs and ceilings is that most of these homes were built with no roof cavity whatsoever and no roof venting. The roof decking is often plank and is exposed on the home's interior as a wood ceiling.

Adding ANY venting in the A-frame roof in a cooling climate such as Wisconsin would result in pouring building heat outdoors in winter and an astronomical heating bill.

Therefore I take a different approach - what follows is my OPINION based on decades of field experience as a builder and building inspector/diagnostician:

1. Find and remove indoor sources of abnormal moisture

2. Use a hot roof insulation design - no venting - combined with very reliable roof covering (I like standing seam metal roofs) since leaks into a hot roof or dense-packed insulated roof usually spell disaster before they're discovered.

3. Install and make intermittent use of one or two gable-end fans to provide outlet venting of the occupied space when needed.

With a removable insulating cover I can remove or hinge-open the cover and run the fans on occasion.

We do not make use of passive venting if it's going to just dump indoor heat outside.

Please use the page top or bottom CONTACT link to send me some sharp photos of the home from outside showing the whole structure from front and side, and from inside showign the area near the ridge and the areas of damage and I will comment further.

What's the best option for a hot roof design in Maine?

My house has a main section in hexagonal shape with 2 wings. The has a hot roof with 8 inches fiberglass bats and 3 in rigid sheets insulation.

Ceiling is 3/4 inch v-match pine boards cut at angles between 6 large beams at the corners of the hex and extending up to the peak where they meet at a large fieldstone chimney.

Condensation appeared two years ago. Building inspector and green contractor suggested taking out ceiling around chimney, where condensation was biggest problem, removing insulation, drying out, spry with foam insulation and put everything back.

Also added range hood, used bathroom fans religiously and kept humidity from 25-50% all winter. Now we are back with the same problem in several sections of the ceiling.

Recommendations are tear down whole ceiling, dry out, spray foam etc like we did around chimney, or caulk all ceiling boards as well as seams at beams, buy a whole house dehumidifier, build a new ceiling with steeper pitch so it is like an attic and vent normally.

I live in Maine and we don't have too many experts in hot roofs so am looking for guidance on which option(s) I should choose.

None are very appealing and all seem costly but I know I have to do something. Thanks for any advice you can give. Tom - On 2016-06-08

Reply by (mod)

Tom, my best advice is

at HOT UN-VENTED ROOF DESIGN SOLUTIONS

Please take a look and then ask any follow-up questions you like.

Would a metal roof be better insurance against leaks and future problems in a hot roof building?

Hello again, We are doing the work as I correspond with you. So your prompt response has been very valuable. I am going to do everything possible to prevent any problem as much as possible.

So the vapor barrier will be installed. What if any specific material would you suggest? Any particular brand and type or alternative would be very helpful.

Also I have un-ventable eves/ soffit. What type of insulation should be used in that area? Would loose cellulose or pink fiberglass be exceptable?

This is a post and beam home built in 1850. So you can imaging the challenges I've been having to overcome. And finally would a metal roof be better insurance against leaks and future problems? Is there any way I could send you pics of the area in question?

If so please explain and I would be very happy to do so. Thanks so much once again. Fred - On 2016-01-06 by Fred

Reply by (mod) -

6 mil poly is fine. As I said it's the cuts, tears, or openings or penetrations such as at light fixtures that will dominate any problem of indoor air or moisture leaking into the roof.

For a DIY insulating project fiberglass, neatly placed to avoid voids and air bypass leaks, is fine. For a professional job I prefer spray foam insulation.

And yes absolutely, a metal roof is in my opinion a superior choice for a well-sealed hot roof design as it reduces the risk of a perforation leak in the roof surface in the future. That's what I put on my own office.

Keep the roof penetrations such as plumbing vents to as few as you can and be sure those are perfectly installed and sealed.
See what can go wrong at

PLUMBING VENT REPAIR 

Do I need a perfect vapor barrier in my home?

In reading HOT ROOF DESIGN PROBLEMS I see you mention "Perfect Vapor Barrier" however I haven't been able to read anything on the subject and what it is actually referring to. I have a non vent able situation. In an sloped roof design.

Using closed cell 4' foam board in between the rafters. their will still be minimal air pockets 1"-2" wide and 1/2" deep on the underside of the roof deck and 1/2"-1" x 12" square areas between the drywall and foam board.

Do I need to fill these shallow areas as best as possible and where and how to I install a "Perfect Vapor Barrier"? Thanks for all your help.. Fred Grassia

Thanks for all that helpful info.... Since I am going to have some voids between the drywall ceiling and the foam board.

Do think it wise to create a perfect vapor barrier? The room will be used in the summer and air conditioning will be in use.

And in the winter the space will be heated on a minimal basis and left a cold space with screened windows crack for ventilation and circulation of air. - On 2016-01-05 by Fred Grassia

Reply by (mod) - Yes - define "perfect vapor barrier"

Fred, thanks for asking.

Perfect vapor barrier is my term for a vapor barrier that has a perm rating of zero AND has no punctures, tears, leaks over the surface to which it has been applied. Metal foils have a perm rating at or close to zero. Plastics and paper are more permeable.

Keep in mind that since the mid 1980's research has shown that the vapor barrier, or even its absence, in a wall or ceiling covered with a continuous material such as drywall, is less important than penetrations in that surface that permit air (and moisture) to leak into the building cavitiy.

The air pockets you describe help you they don't hurt. It's penetrations in the ceiling that would be a concern.

In my OPINION, because a hot roof design can trap moisture and damage the building, having the best vapor barrier you can achieve is worth the small extra expense, but don't forget that an opening anywhere is able to overwhelm even a perfectly-placed foil vapor barrier; And if the roof leaks from above, that water entering the roof cavity is going to stay therein and be a problem.

I don't think the voids you describe argue for or against the vapor barrier, as they are not what will cause water or moisture to be trapped in the roof cavity.

...

Continue reading at HOT ROOF DESIGN PROBLEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HOT ROOF UN-VENTED ROOF FAQs-2 - a lengthy roof ventilation discussion between reader Dave and moderator Dan

Or see this

Article Series Contents

• CATHEDRAL CEILING INSULATION
• HOT ROOF DESIGN PROBLEMS
• HOT UN-VENTED ROOF DESIGN SOLUTIONS
• HARD to VENT ROOF SOLUTIONS for HIPS & CATHEDRAL CEILINGS

Suggested citation for this web page

HOT ROOF UN-VENTED ROOF FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING VENTILATION

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