Hot roof design problem solutions:

This article 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.

This article series about roof and ceiling ventilation describes inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems in buildings.

Solutions for un-vented roofs: Avoid cold-climate ice dam leaks & reduce cooling costs in hot climates

Ice Dams on Un-Vented Roofs in Cold Climates

Grange and Hendricks (1976) recommended a combination of eaves and ridge venting to avoid ice dams on buildings.

Other authors found that ice dams seldom occur at temperatures above 22 degF. or when attic temperatures are below freezing.[7]

Our photo shows an ice-dam prone roof on a tall building with a slate roof.

1. Roof Edge Sheathing Intake Vent: There is a product called Hicks Starter Vent™ and similar products such as the SmartVent™ distributed by DCI products that replace the first few inches of roof sheathing under the shingles or slates by a louvered vent so that air can sneak into the roof cavity by that path.
   
   It's cost-appropriate to install this when re-roofing but probably too costly to do so otherwise.
   
   See details at ROOF VENT if NO SOFFIT
2. Half-Ridge Vent: a half-ridge vent, basically a conventional ridge vent but cut in half lengthwise, can be installed at the up-roof edge where a lower roof abuts a higher building wall, such as where a roof slopes up to butt against the wall of a raised dormer.
   
   Combined with soffit intake venting this roof vent design works well to cool and dry roof sections with this shape.
3. Ice and Water Shield: On roofs that are too difficult to vent, a second-best solution is to remove the shingles (or slates) from the lower 3 feet of those slopes where leaks and ice dams have been recurrent, install a waterproof but nail-able membrane such as WR Grace's Ice and Water Shield (other product names from other manufacturers) which will prevent any ice dam backup leaks from entering the building.
   
   This is basically a sticky membrane that is applied to the roof decking and through which shingle or slate nails can be nailed back onto the roof; the membrane seals around the nails so that those penetrations do not form leaks during a water or ice backup.
4. Adding Attic Insulation to Avoid Ice Dam Leaks: Indoors, unfinished attic: if we add as much insulation as we can fit into the attic floor of an unfinished attic space, paying close attention to insulating under the eaves at the lower roof edges, and making sure that the insulation blanket is absolutely complete with no missing areas or holes or leaks, we can reduce the heat loss into the attic space and thus reduce the warming of the roof underside and thus reduce future ice dam formation and its related leaks.

   It's better to place insulation in the attic floor than under the roof, since in the latter location ventilation and drying of the roof sheathing are prevented and there is a greater chance of future mold growth or rot caused by trapped moisture there.

5. Un-Vented, Hot Roof Designs Indoors, finished attic: Where the attic space is finished with drywall or other ceiling materials installed against the underside of the roof rafters, while I prefer in-floor insulation, here we'll have to insulate the roof cavity between the rafters.
   
   In cases where there is no under-roof venting system (no soffit intake vents, no ridge vents), a "hot roof" design is followed: the roof cavity between rafters can be filled with insulation, followed by installation of a perfect vapor barrier, followed by finish surface of drywall or whatever else.
   
   The vapor barrier and air sealing in particular, need to be perfectly installed to prevent warm moisture-laden air from entering the un-vented roof cavity. But even so, see Worries about the "hot roof" un-vented Cathedral Ceiling Designs, discussed below.
6. Tips for insulating a cathedral ceiling, take care to seal ceiling penetrations such as around light fixtures or ceiling-mounted hard-wired smoke detector. More moisture enters building cavities through these cuts in the ceiling (or wall) drywall than permeates through the drywall itself.
   
   While fiberglass insulation is an excellent and effective product for insulating most building cavities, in areas where there is extra risk of trapping moisture (and thus rot or mold infections) such as crawl spaces and cathedral ceilings where roof venting may be absent or minimal, we prefer to use closed-cell foam insulation products or spray-in icynene foam insulation: these products can seal the cavity against drafts and they do not as readily pick up moisture nor do they readily form hidden mold reservoirs.
   
   See CATHEDRAL CEILING INSULATION
   
   and INSULATION LOCATION & QUANTITY for ATTICS
   
   See FIBERGLASS INSULATION MOLD
   
   and MOLD RESISTANT CONSTRUCTION for details.
7. Use of roof de-icing cables or heat tapes to avoid ice dam leaks is described
   
   at HEAT TAPES & CABLES for ROOF ICE DAMS.
   
   While we prefer to avoid ice dam leaks by good building design and good under-roof ventilation, where conditions require stopping ice dam leaks on an existing structure, proper installation of heating cables may be the fastest and cheapest solution.

Our expert Steven Bliss commented to offer a final word on Hot Roof Designs:

I agree with you that, in the real world, this is not such a good idea. If there's a flashing leak or other roof leak, you could have a pretty soggy mess that stays wet for a long time and could cause structural decay.

Plenty of people are building hot roofs, but I wouldn't -- except maybe one with spray urethane which won't absorb much water like cellulose would. [37]

 

---

---

ADVERTISEMENT

---

---

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020 09 15 Mod said: Rx for fouled up roof

I've ducked offering a specific repair, Mile, because I'm not confident I underdstand what materials are present nor how the roof is actually constructed. Perhaps you could post a photo or sketch (one per comment).

We need:

- supporting structure
- decking to which roofing shingles or whatever are nailed
- insulation

If the fiberboard that was cut out and removed was serving as both nailer and insulation then just foaming the space wont' work. So you'd need to remove enough roofing to expose all of the improper repair, insulate the roof cavity, provide a nailer, then restore shingles.

About the concern for temperature variation and moisture or condensation in the roof cavity, there's a good chance that the problems you have seen are from indoor (warm moist) air leaking into the roof cavity, not merely a lower R value for the fouled-up area.

On 2020-09-14 by MileHigh

The roof does NOT have a ridge vent. When the roofing company was hired to replace the old asphalt shingles because of hail damage, they cut through EVERY SINGLE LAYER of material down to and including the ceiling T&G planks. They also did the same thing to put four intake vents in the lower area of the roof on both sides - two on each side. The reason is simple: the crew the roofing company sent here apparently did not know what they were doing or they had it mixed up with a different project because the new code calls for more vents. What they clearly did not realize is that the additional vents were needed in the other area of the house where there is an attic. It is an unbelievable nightmare.

The insulation is fiberboard, a pretty thick one. The house was originally built in the mid 1970s. When the roofers became aware of their mistake, the roofing company did the "repairs" but they used a cheap rolled fiberglass bat insulation. Unfortunately, the temperature in that part of the house has changed significantly and we saw ice dam forming all around the house for the first time ever.

We are still trying to figure out what the best method of repair will be to restore the insulation protection (or improve it) so that the comfort level is back to how it was and to avoid the formation of ice dam. The easiest access is clearly from the top by removing the roofing materials to apply whatever type of insulation will replace the fiberglass bat. The big question remains what will be the most effective type of insulation to use and what will be the best way to apply it?

On 2020-09-13 - by (mod) -

So can we get straight on what we're talking about here? Are we talkin about solid foam or are we really talking about fiberboard. In the 1960s it was not uncommon to use very thick 2in or so I reward panels that serve both as insulation and decking and sometimes we're even left Exposed on the inside. I've documented those on a 1960s house in Two Harbors Minnesota. Repair methods you would choose for probably differ but in any case it may be possible to remove the fiberglass and foam the cavity where the roof was over cut.

I don't understand why we have a ridge vent or any kind of vent on that roof.

On 2020-09-13 by MileHigh

Just to clarify, instead of foam board, what we have was described by the inspector as "fiber board"

Thank you, Dan. That is exactly what we have and when they screwed up and cut through the entire length of the ridge to put a ridge vent on the roof, they also cut through everything including the insulation. They did the same thing on four different places in the lower part of the roof where they installed intake vents and removed them when they realized their major mistake.

The problem is that they just put in rolled bat insulation which clearly has much lower R-value because we had ice dams all over the roof which we never had for almost 20 years. The house has been hotter in the summer and colder in the winter than usual.

What is the best way to "repair" this roof to stabilize the temperature at least to how it was (or even better) and also to avoid the formation of ice dam which surround the entire house like ice curtains.

On 2020-09-11 - by (mod) -

Mile:

The photo to which you refer - shown again below - is of a home with exposed wood planks on a cathedral ceiling; in this type of construction the usual method of insulation is the application of solid foam board insulation atop the wood planks, over which roof decking is nailed, through the insulation and into the rafters; then the rest of the (un-vented) roof covering system is installed. Spray foam is not normally used in those designs.

On 2020-09-11 by MileHigh

Thank you for your reply. What if there is no access to spray from inside? The T&G ceiling planks are sitting on top of the rafters and the rafters go all the way to the structural ridge beam. So, what we have is a lot like one of the pictures you have here on your site at this link - the 1st & 4th photos at this link

https://inspectapedia.com/structure/Cathedral_Ceiling_Roof_Framing.php

It is my understanding that the foam should be sprayed on the bottom side of the roofing deck but how does it get applied in this case?

On 2020-09-10 - by (mod) -

I like closed cell foam, but have used both that and open celled, sprayed up under the roof deck from inside is common; in all cases it's essential that the roof covering be as bulletproof as possible as water leaking into any hot roof is asking for hidden damage, rot, mold, etc.

Sorry we can't make a specific referral; use someone who has done the work and check references.

On 2020-09-10 by Anonymous

Thank you for the ideas and suggestions.

We are in the final lap of our adventure with our roof issue. I have a couple of questions: 1) Based on your wealth of experience, what do you recommend we should use as insulation after we get rid of the rolled fiberglass bat insulation? They have cut the rigid insulation (some type of rigid fiberboard) the entire length of the ridge as well as in four other locations where they cut in the lower areas of the roof to put intake vents. Closed cell foam is what a couple of contractors have recommended - do you think it will work using the closed cell spray foam in the areas where they cut out the rigid insulation? If so, where is the best place to spray it on? I have read on here somewhere that one of the recommended ways is to spray it on the inside/bottom of the roofing deck. We have not found a lot of contractors who have actually done this type of work - spray foam insulation for cathedral ceilings which leads me to my next question......

2) Do you have anyone you can recommend for this type of project with the experience? That has been one of the most challenging parts - finding a contractor with experience on this type of project. Many want to redo the whole thing and not just the areas where the old rigid insulation was cut out. Almost all of the contractors we found on "new" construction and lack the experience of a repair/rehab project with many not even wanting to do it.

Any thoughts/ideas/suggestions you are willing to share will be greatly appreciated. Given that we were hit with a lot of delays due to COVID, our goal is to get it done before the winter snow arrives. As always, I appreciate you sharing your knowledge and thank you for it.

On 2020-05-29 - by (mod) -

Mile

IMO that's ridiculous.

Any professional forensic investigator knows how to proceed, with permission, documentation, protection of the building, etc. even if access wants to be from the roof above, removing, cutting, then repairing the roof. More likely the inspectors know that they're not equipped to actually DO a roof repair to be sure to leave you with a roof that's not leaking.

That means we need to find both a courageous experienced inspector AND a roofer to be sure the repair is sound afterwards.

And the nightmare continues: the roofer may not want to get involved if she knows you are in dispute with one of her (or his) comrades.

Patching foam insulation with more spray foam is trivial, open or closed.

On 2020-05-28 by MileHigh

Thank you, Dan. It has been a nightmare already. Many inspectors are afraid to open up the roof out of concern to not be blamed by the roofing company for opening it up. There is no access from the inside/ceiling side because the T&G planks are sitting on the rafters. Assuming we get someone to open it up and we confirm we have a mix of the old rigid insulation along with the new rolled R-15 insulation, what is the best way to bring it back up to snuff or better? The same type of rigid insulation is no longer made and the type they put in to cover things up is not effective and does not comply with code. If there are no other issues besides the poor insulation along with the old rigid one, what would you think is the best way to insulate? Get rid of the rolled R-15 and apply closed cell foam insulation? Start anew with other type of rigid insulation? The way it is now, we noticed when we had frost, it is easy to see where the new and inferior insulation is and where everything else is.
Again, thank you in advance for all your responses and ideas.

On 2020-05-27 - by (mod) -

Mile

Sorry for everyone involved in this snafu; In my experience you may drown in a sea of arm-waving "expert witnesses", attorneys, and endless legal fees not to mention the aggravation of a dispute like this one.

Instead, let's cut trough the speculation and simply have an expert open the ceiling, inspect the conditions there, photo-document everything, and then diagnose what's been happening and what is the best repair.

If fail to actually inspect the in-ceiling conditions you may find that you settled for a repair cost amount and then discover that you actually face a much greater cost to remove moldy materials, clean the roof cavity, and rebuild.

On 2020-05-27 by MileHigh

Recently, a roofing company was replacing hail damaged roofing at our property where we have a cathedral ceiling on one section of the house. Believe it or not, the roofing company cut right through every layer of protection down to and including the ceiling, which is T&G wood plank. When asked what in the world happened, they said they were going to install a ridge vent and did not realize it was a cathedral ceiling. The original setup was rigid insulation that provided pretty decent protection against the summer heat. When the roofing company "repaired" the damage, they put in rolled fiberglass R-15 insulation and covered everything back up quickly. When asked, they said they replaced it with the same type of insulation. When we got into the cold season, there were so many ice dams that we had a curtain of ice all around the property suspended from the gutters and fascia and the house was much colder in that area and heating expenses were noticeably higher. In more than a decade in the house, we have never had an ice dam, ever. Now that we are in the warm season, it is much warmer than ever and cooling expenses is already higher. We are about to enter the litigation phase now and we are trying to figure out what the best way to address the proper repair to the cathedral ceiling will be. Since the rafters are exposed on the inside, there is not much room for the fiberglass type of insulation. On here, I have read about closed cell foam and other similar types of insulation that will help avoid the issues we have been able to avoid until now - never any leak, no mold, etc. Looking for suggestions of good ideas that will also be in compliance with the current code of having at least R-30 insulation with recommended R-45. Thank you, in advance, for your ideas and suggestions.

On 2019-06-11 - by (mod) -

I'd like to help but I don't understand the terminology that you've been told. I don't know what a roof exhaust edge Vent is. Perhaps they mean some fan operated vent.

On 2019-06-09 by Ron

Reroofing a north-south 3/12 sandwich roof, no attic. Currently east-west ridge vented with baseball sized soffit vents every 16 inches on both north and south soffits. Roofers want to upgrade the ridge vent and several are offering roof exhaust edge vents. Roofers disagree about whether they should be used. What is your opinion on these? What would be your recommendations for best venting options overall? Would you replace the ridge vent or soffit vents, which would incur some expense?
We are in Denver CO, where we have extremes of snow and cold weather, hail, and heat and warm weather. High humidity and mold are not a factor in our dry climate.

On 2017-10-23 - by (mod) -

Brady, please post just once - avoid doubling our work. Thanks.

See CATHEDRAL CEILING INSULATION https://inspectapedia.com/insulation/Insulate_Cathedral_Ceilings.php

On 2017-10-23 by Brady

am looking for best route to go. Heres the case. Thanks for your help if possible.

A mud room between house and garage. The ceiling was vaulted into catheridal ceiling. With tounge and groove knotty pine boards. Between boards and roof decking is fiberglass insulation packed between roof and knotty pine. No vapor barrier between the two. No longer a sufficent venting system between the soffit and ridge vent. Removing tongue and groove is not an option. My thought was to have the problem taken care of from the outside. Have someone remove shingles. frame over old roofdeck with 2×4's spray 2" of closed cell spray foam. Ply wood on top. Lay new roof. Remove ridge vent close soffit vents seal where roof meets walls. Would this be possible to prevent moisture issues in summer / winter. And would it help remove heat loss. Looking for quote and advice. It is about a 600 sq ft section i would this done to. Located southren wisconsin. Thanks for your help

...

Continue reading at INSULATE ROOF with SOLID FOAM BOARD + AIR SPACE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CATHEDRAL CEILING VENTILATION
• CAPE COD ROOF & KNEE WALL INSULATION & VENTILATION
• CATHEDRAL CEILING INSULATION
• HOT ROOF DESIGN PROBLEMS
• HOT UN-VENTED ROOF DESIGN SOLUTIONS
• HOT ROOFS in HOT HUMID CLIMATES
• HOT ROOFS vs VENTING in COLD CLIMATES
• HOT ROOF DESIGN vs LEAK RISKS
• HARD to VENT ROOF SOLUTIONS for HIPS & CATHEDRAL CEILINGS
• ICE DAM LEAKS
• PROBLEMS with PARTIAL ROOF VENTILATION
• ROOF FRAMING TIES & BEAMS proper framing of a cathedral ceiling
• ROOF ICE DAM CURE: Comparing Two Houses
• ROOF NOISE TRANSMISSION
• ROOF VENTILATION SPECIFICATIONS pros and cons of hot roof designs

Suggested citation for this web page

HOT UN-VENTED ROOF DESIGN SOLUTIONS 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

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---