This article series describes roof venting problems and solutions:

Ice dams, attic condensation, attic mold, and inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems in buildings. It describes proper roof ventilation placement, amounts, and other details.

These recommendations are based on many years of building inspections, on the observation of the locations of moisture, mold, ice dams, condensation stains, and other clues in buildings, and on the correlation of these clues with the roof venting conditions at those properties, and frequent literature review and professional discussion.

We have also measured changes in airflow, temperature, and moisture before and after installing roof venting.

Q&A on How to Stop Roof Ice Dam Leaks

These questions & answers about the causes of and cures for roof ice dam leaks were posted originally

at ROOF ICE DAM LEAKS - home - so that's a great place to start reading about what to do about ice dams and blockages on your roof.

[Click to enlarge any image]

On 2019-01-04 by (mod) - limited under-roof access on doublewides

Many doublewides have no indoor attic access as the under-roof space is very limited.

There might be outdoor access from a gable end on one or both ends of the home.

About opening up walls to add insulation, before considering such an approach you need to inspect the current insulation: is the wall cavity already filled? If so you can't add insulation.

And if your interest is reducing heating or cooling costs, before adding insulation the first priority is stopping drafts, air leaks.

See ENERGY SAVINGS PRIORITIES

On 2019-01-04 by Lynn 1984 Chancellor double wide, cannot find access to the attic

I can be reached at attune@telus.net for a response to my previous comment. Thanks

I live in a 1984 Chancellor double wide, and cannot find access to the attic, I cannot find any info on R rating at that time of build, or insulation top, bottom or walls.

I want to open up each accessable wall which has panelling to add better insulation, should I replace with dry wall or return panelling?

I also have metal siding, noticed you did not like cellouse type, what them? I thought of the safe and sound one as I think it is fireproof? Any place I can find info on my house?

On 2018-04-27 19:41:55.649864 by (mod) -

Great, do keep us posted - what you report will help other readers.

On 2018-04-24 21:17:40.414156 by Anonymous

I certainly will update this tread once I have more input after the inspection next week. The new guys seem to have more methodical approach, first we inspect and test the site, then we talked about solutions.

This is a very bitter lesson to learn.... I did have my qualms about the existing installation but the myriad of conflicting opinions and solutions crated such a fatigue that I let my judgment slip.

Should have taken my time to see how the house performs over the winter with the new roof on and give myself more time to find a experienced contractor.

On 2018-04-24 19:51:31.812420 by (mod) -

Blower door tests are interesting and of course everyone who has a blower door likes to use it.

However that test is not prescriptive nor diagnostic except in a very general way.

A visual inspection along with thermography or infrared will probably be more helpful and finding and fixing air bypass leaks.

I would like to see the thermography report and the blower door test report

On 2018-04-24 17:57:47.394358 by Anonymous

Thank you for your response Dan.

You are very much tight about the lack of uniformed approach to the insulation vs ventilation issues plaguing the Cape style homes.

My best bet at this point is that the air-sealing was not adequate and the warm interior air was leaked around the opening of the access panel thus the majority of staying/mold presence on the rafters slope directly across it.

I am having another contractor coming out to do the door blower and infrared imagining testing. In the meantime, I will re-read the articles suggested by you.

I am hoping there is no serious damage enywhere else in the roof/attic structure and I managed to catch the problem before it became epidemic.

Thank you again for taking time to help out. Very much appreciated.

On 2018-04-24 15:05:43.249260 by (mod) -

llona, it sounds as if it'd help you to review the article ROOF ICE DAM LEAKS

as well as ROOF VENTILATION SPECIFICATIONS

That article series includes solutions for hard-to-vent roofs that include some cape style homes.

Venting of attic or roof spaces is not implemented uniformly in all climates. In some Minnesota homes I see people focusing less on attic venting (perhaps because deep snow cover obstructs ridge vents) and more on

- eliminating air leaks into the attic or roof space

- assuring complete, uniform, adequate insulation

Watch out: some of our winter time under-roof photos show frost, not mold, though of course that moisture (when the frost melts) can show up later as leaks into ceilings below or as mold contamination of insulation or ceiling drywall.

On 2018-04-24 03:33:40.689914 by Ilona, MN

Hello,
I am afraid I am having a major problem developing in my house and I am getting more and more confused as I try to research/find info what to do next.
We own 1948 Cape style house (11/2 story) in Twin Cities, MN.

After many years of living in the undeinsulated home, we decided to hire a contractor to insulate the upper floor.

We had no soffits or any way to install them, no gable vents, nor ridge vent.

There were a few few square venting boxes at the back of the house but nothing on the front roof.

Yes, the living space upstairs was cold in winter and hot in summer.

Due to the lack of venting the contractor proposed to airseal all the small attics behind the kneewalls, densely packed cellulose was pumped into the rafters of the slanted ceiling ( 2x6 rafters, no air channels), about 6in of cellulose under the floor boards in the attics, followed by the blown in loose cellulose( 18in)

The kneewalls were covered with unfaced r13 bats wrapped with a house wrap

Per certified and licensed insulation contractor, it was more important to seal and insulate the attic than provide the ventilation considering ten existing structure.
Shortly after this was completed, we had a new roof installed with a proper ice and water shield as required by the code.

No ridge vent was installed at the time since we did not have any way to provide adequate air intake at the eave, etc.

Winter was harsh with higher than average snowfall but we barely had any icedamning. I sure was pleased, still did the roof raking though. The upstairs was cold so we used a portable heater to warm it up with the plan being to install a split system down the road.

The Cooling/heating vents going to the upper floor have been shut and sealed off when we installed the insulation.
Fast forward to today, went to check the attic after the winter as it was getting really warm upstairs.

Removed the access door in the kneewall to find quite a bit of staining on the rafters and joists as well as what definitely looks like your pictures of the white mold!

Never had that problem before...I am utterly devastated and panicked that we are looking at possible continued problem and damage to the rafters.

I have met with several insulation contractors when planning the insulation and they all had different proposals how to deal with the 11/2 story home. I have spent countless hours trying to research in my own and was further confused.

So, what could I do now to mitigate the issue? How do I deal with the obvious condensation and moisture in the attics? I did try to contact the contractor and have not heard back yet. I might need to resign myself to dealing with the issue on my own.

I have the residing job coming up and it was suggested that I should install gable vents on each end of the side walls and remove the insulation from the rafters above the finished living space ( the slanted ceiling, drywall on the interior).

The roofer mentioned installing a bunch of small venting boxes but I am not convinced it is the best solution?

Any feedback would be greatly appreciated, I could use some very concrete advice as to what to do within the existing structure. This is a very depressing development and the source of incredible stress in our family...

On 2017-12-30 00:38:10.935306 by (mod) -

Moldy insulation, possibly rotted sheathing or othet w ood components.

Take the opportunity to follow the water stains and you will know for sure whether there are any remaining active leaks

On 2017-12-30 00:32:49.166000 by Amateur Mac

Old roof leak/now efflorescence on siding -

We replaced a leaking roof on manufactured home several years ago - had water leaks at several windowsills and fixtures.

To prevent future leaks, we used ice dam material on the entire roof (3:12 nominal slope) This was done during July, which is hot and dry in the Pacific Northwest.

A couple of years down the road, we began to see efflorescence on the HardiPanel siding on one corner of the house.

I am sure there is moisture in the wall, though nothing is visible on the interior sheetrock.

It has been several years now since the roof was redone. The efflorescence is still present, but reduced.
I plan to open up the wall this summer... any idea on what we might find?

On 2016-10-22 19:33:22.472644 by (mod) -

"Must" clean off mold - depends on the situation.

Trivial amounts of mold or even large amounts of cosmetic mold are not likely to be harmful to building occupants. But sometimes there are causes of air movement down from an attic or roof space into occupied space, such as when air conditioning is cooling lower floors in a building.

If there are large areas of harmful mold in an attic I would clean the surfaces, seal them, and replace insulation exposed to airborne mold contamination.

On 2016-10-22 19:25:31.543239 by Madelyn thomas

Must I have mold cleaned off attic sheathing after moisture problem corrected?

On 2016-08-16 18:46:36.814461 by (mod) - inadequate venting, the little Dutch Boy at the dike

Anna

I'd want to do a bit more diagnosis: is there an existing footing drain system outside the walls? Is it blocked or working? How old are the home and the drain system?

Moisture can condense on cool basement walls if the basement air is humid even if there is no water entry into the structure at all. If that were the case I'd be looking for an indoor moisture source and perhaps I'd look at full time dehumidification.

Mold may grow behind a plastic membrane, certainly I've seen that; if the membrane is sound it's also reducing the ability of particles to come into the building but of course the best approach is to design the building so it's not growing mold rather than growing mold and trying to contain it.

B-Dri type interior trench and drain and wall barrier systems can stop water from going onto the basement floor and if the whole wall is covered and sealed at wall top, can probably significantly reduce the movement of moisture into the interior space. It's a last-resort plan that may make sense when properly fixing the problem outside is deemed far more costly.

Picture the little dutch boy at the dike - stopping the water at the last possible second.

In 98 out of 100 homes I inspected over nearly 50 years in the field, the wet basement problem could have been cured from outside, and in 75% of those the problem was originating at the roof/gutter/downspout drainage system.

Even when people assured me over the phone that the gutters were working I often found that in some areas they weren't.

On 2016-08-16 12:39:48.268393 by Anna

Hi Dan,

After thinking about your comments and looking at our site, I think we definitely need to try to divert runoff outside our house. In order to have a completely dry basement though, we will probably need to have a perimeter drain and plastic sheeting as well.

I say this because moisture seeps through the walls even on the side of the house that has excellent grading and gutters.

We are pricing out our options and have a couple of quotes from companies that install B-dri type systems.

I am concerned that mold could form between the heavy plastic and the block wall that it is fastened to. As I mentioned, our basement walls are always a bit moist, even on the sides that are properly graded.

Do you believe mold could be a problem behind the plastic membrane?

Thanks,

Anna

On 2016-06-12 21:29:26.501920 by (mod) -

I like swales to conduct surface runoff away from a building when the site is crowded and we can't simply grade away.

At problem buildings such as a metal roofed barn-conversion on which owners couldn't keep gutters (snow country) we buried drainage mats that conducted surface runoff to a drain system that conducted water along a swale ultmately to daylight.

Depending on the volume of water anticipated AND the probability that there is subsurface as well as surface runoff, it may be appropriate to excavate and install drain piping and gravel at a deeper depth before finishing the swale; that can also act as an intercept drain keeping uphill runoff away from the building.

Ledge rock is a special problem: if the rock is sloping towards a home foundation wall it is *very* difficult to keep water out of the basement unless you intercept that water at and above the rock surface and carry it away.

I don't understand the thinking nor terminology of your energy auditor;

And I do not agree with the casual remark that a little basement water is ok. It is not ok, it is never OK and it would be very unusual for me to inspect an older home that had "a little basement water" that had not, over its life,

had more than a little water as conditions varied or worsened; water under a home travels up through it inviting problems as high as mold and condensation under the roof deck.

A last resort is an interior trench and drain system around the basement; B-dri type systems run heavy plastic up the walls so that water running down a wall goes into the drain system not into room air. It's not my first choice as I prefer keeping water out rather than letting it in and then getting rid of it.

DO NOT insulate over wet walls; in particular fiberglass would be a mold catastrophe; first fix the water problems.

Then if you want to insulate the walls use closed cell solid foam.

Expansive clay soil deserves special attention as you understand; in some locations people actually add a watering system - the object is to keep the clay at a constant volume; what's needed depends on where you live.

Houses are not built to be boats with a waterproof hull

; if we need to make the house more waterproof and IF we can't fix the problem by proper control of roof and surface runoff, it may be necessary to excavate, expose foundation walls, install geotextile drainage mats and a drain system to daylight, then backfill. Beware of excavation close to a block foundation as an inept contractor can collapse the foundation wall.

On 2016-06-11 23:20:43.864563 by Anna

Thanks so much for your prompt response, Dan.

I have a follow up question about drying out the crawlspace/basement:

We have a basement that is poured concrete over ledge sloping from about 2 feet on one side of the house to full basement on the other. On one side of the house is negative grading, and the property line is 10 feet out from the foundation.

This is the side of the house with concrete over ledge 2 feet below our floor joists.

The other side of the basement has steeply sloping grading away from the house.
We have expansive clay soil that exerts a tremendous amount of hydrostatic pressure, enough to have buckled a partially below grade wall on our attached garage. (another problem!)

During rainstorms, we have water trickling down the ledge as well as coming under the walls and through cracks in the concrete block. All walls are covered with efflorescence. Water comes in along the walls with good grading too, but we don't have adequate gutters so that could be a cause.

Every house in our neighborhood has varying degrees of basement moisture.

Our plan is as follows, based on info from this site:

Dig a swale as deep as we can (considering the ledge close to ground surface) 10 feet from the house on our property line and correct the grade from there to our house. Possibly put a drainage pipe in the swale.

Add gutters all around the house and direct downspouts away from foundation.
If this doesn't work, consider an internal drainage system.

Energy auditor wants to put a French drain along the exterior of the basement wall on the negative grade side of the house without doing grading work (because of the space constraints).

He says that a little bit of water in the basement is not a problem, and he will leave space at the bottom of the foam board insulation so the water can escape. He says a basement window fan will improve air quality.

We are concerned about putting insulation over wet block. We are concerned that drains and gravel against the foundation might invite more water considering our clay soil and the negative grading.

The window fan sounds good, but we noticed the info on this site about sealing crawlspaces from outside air, and wonder if this info applies to basements like ours that are partially crawlspaces.

Thanks again for your helpful response to my last question.

On 2016-06-10 23:38:11.673227 by (mod) -

Thanks for the nice comment, Anna; we work hard to provide accurate, unbiased data and we're thrilled when a reader like you finds it useful.

I'm not sure I agree with your energy auditor, and if that person's expertise was close to some of the energy auditors I've worked with, I'd take that arm-waving with a grain of salt.

He's basically converting your home from a traditional "vented" attic to a "hot roof" design. I'm reluctant to do that on an older home using a full attic, as too often defects in installation or leaks that occur over the life of the "retrofit hot roof" become a rotted disaster.

I don't think the auditor understands air movement, or didin't communicate it clearly either.

If we provide PROPER attic ventilation we have continuous intake at the soffits or eaves and continuous outlet at the ridge - not blocked anywhere. That gives us about two times as much lower roof opening for air to enter as the exit opening along the ridge.

In turn that ratio helps assure that when air escapes out of the attic it does so by pulling in new outdoor (dry in winter) air through the eaves or soffits, rolling that air up the underside of the roof decking, cooling it and drying it.

Those conditions prevent ice dams as well as attic condensation, moisture and resulting mold.

I would consider a "hot roof" design in a cathedral ceiling roof, with a ceiling with no openings to leak air into the roof cavity, but even then I prefer to cover such roofs with the most-durable, leak-resistant roof I can , such as standing seam metal roofing.

Also you want to dry out that wet crawl area; leaving that moisture to travel up through the home (and collect under the roof) is asking for rot and mold troubles.

Search InspectApedia for CRAWL SPACE DRYOUT

to read a series of articles giving various options; it's always best to get the water away outside before it enters the crawl area; if you absolutely can't do that you may have to install an internal trench and drain and maybe sump system.

On 2016-06-10 21:10:24.179290 by Anna

Forgot to add: We also have a wet crawlspace/basement that will be very difficult to fix due to improper grading from a neighboring property that slopes directly to our house. We own 10 feet out from the foundation. From reading on the site, it seems possible that this is part of the cause of our attic mold.

On 2016-06-10 21:06:29.913634 by Anna

Hello,

I have been reading this site for a while and have based many home improvement projects on your recommendations. Thank you for this source of information.

Last year, we reroofed our hip roof ranch and added a ridge vent.

Our house is in Vermont. We have a single gable in the middle of the house and it has a gable vent. We also had a couple of small rectangular soffit vents on each side of the house.

Over the winter, we noticed ice damming and increased mold (there was some already present before the roofing project) on some areas of the attic sheathing. This spring, after consulting this site, we installed continuous soffit venting at the outermost edge of the soffit.

We plan to cover the gable vent, but first we intend to redo the ridge vent because we realized that the roof decking was never cut to allow the ridge vent to actually work.

So right now, our attic is vented through continuous soffit venting and the gable vent, although a non functioning ridge vent is in place.

We recently had a home energy audit, and the contractor doing the audit said that we need to cover the soffits (including vents) with fiberglass insulation and then blow in cellulose. He says that soffit venting causes more problems than it's worth, especially over windows where it can vent escaping heat into the attic.

He said that no attic venting is needed. This seems contrary to everything we have read on this site. Does he have a point? Is his advice somehow best practice in the northeast, or should we look for another contractor?

I hope you can clarify this!

Thanks,

Anna

Question: reader claims drip edge prevents ice dam formation

(Aug 14, 2014) TrueNorth said:

IMHO, this article is academic hog wash, irrelevant and points the homeowner in the wrong direction because it fails to explain the real reason for many homeownes. The article neglects to mention a cause of ice dams is faulty roof installation, where drip edge flashing was not installed.

Reply:

Really? Thank you for your opinion True, but with respect, you are quite mistaken - let's not confuse your opinion with the combination of fact, research, and expertise given by generations of roofers and by folks who have inspected many ice dam problems in a variety of environments.

The data in this article series is based on expert sources not theoretical speculation.

Ice dams form on the cold lower edge of a roof as water from melting snow or ice higher on the roof runs down and hits that cold edge.

Ice dams can become large enough to cause water to back up under shingles even several feet back up the roof slope as well as causing water to find its way into the building by way of soffits or at other points.

A fundamental understanding of why ice forms on lower roof edges may be helpful. It is heat loss that melts snow on upper roof areas, followed by that meltwater running down to the lower and colder overhanging roof edge where it freezes to ice that causes ice dams.

Faulty drip edge flashing or perfect drip edge flashing has nothing to do with ice dam formation except in the uncommon case of the combination drip-edge and Hicks Starter vent that provides intake venting at some roof edges.

For buildings where ice dams are a chronic problem or are unavoidable because of roof, insulation, and ventilation design limitations, the use of an impermeable barrier such as ice and water shield extending well up the roof from its lower edge may permit living with ice dams without leaks into the roof or wall cavity.

But no ordinary metal drip edge flashing can prevent ice dams, nor prevent ice dam leaks.

Take a look at the other ice dam articles in this series for more details.

Also see ROOF VENT if NO SOFFIT

Question: Ice dam leaks on new home

(Feb 27, 2015) chris said:
I recently moved into a 30 by 60 modular home 1500 square feet! the house smell musty like mold

but I just thought it was because the house was just remodeled and the air was on 50 deg! after moving in I went up into the attic and the north side roof and gable end was soaked with wetness and had signs of mold! the eastside was dry!

I called two different contractor and both said the ridge vent was bad so paid the money and had it replaced! after a week I went back up and still soaked and now it had frost on the osb! the house has full eve vents with baffles that are not blocked and a fully full ridge vent!

I cant for the life of me figure it out. I think its the crawl space the is a sump and the grounds not covered with plastic sheeting there is no hvac in the attic its in the crawl space! I leaning towards the crawlspace being the cause! what does you all think! please help before my house is destroyed

! I have pics if it helps I can text them if u would like to see!

I forgot to say that the house gable end on the northside was running with a tea color down the siding! the house is a ranch style and was manufactured in 2002!

Reply:

Chris

Our email is at the CONTACT link at page bottom. Seeing some photos may let me comment more usefully. Imagery that a wet crawl area can send water up through a house, especially if the water or moisture is being picked up by the HVAC system.

...

Continue reading at ROOF ICE DAM LEAKS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Roof Ice Dam Articles

• ROOF ICE DAM LEAKS - home
  • HEAT TAPES & CABLES for ROOF ICE DAMS
  • HEAT TAPES & DE-ICING CABLES on FLAT ROOFS
  • ICE DAM LEAK EMERGENCY REPAIRS
  • ROOF ICE DAM DIAGNOSIS
  • ROOF ICE DAM CURE: Comparing Two Houses
  • ROOF ICE DAM PREVENTION at SKYLIGHTS
• ROOF VENTILATION SPECIFICATIONS - home
  • ROOF VENT SOFFIT + RIDGE NEEDED
• ROOF VENTING DEFECTS

Suggested citation for this web page

ROOF ICE DAM LEAK 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

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

Ask a Question or Search InspectApedia

Questions & answers or comments about how to diagnose and fix attic moisture, condensation, and mold sources

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.

---

 

IF above you see "Comment Form is loading comments..." then COMMENT BOX - countable.ca / bawkbox.com IS NOT WORKING.

In any case you are welcome to send an email directly to us at InspectApedia.com at editor@inspectApedia.com

We'll reply to you directly. Please help us help you by noting, in your email, the URL of the InspectApedia page where you wanted to comment.

Citations & References

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

---

ADVERTISEMENT

---