Questions & answers about the impact of blocked soffit vents on building roof cavity or attic moisture, condensation, ice dam leaks, mold.

This article series xplains the effects on buildings caused by locked soffit intake vents and we explain how blocked soffit venting causes or contributes to attic condensation, moisture, and potential mold contamination problems in buildings.

Blocked Soffit Vent Intake Questions & Answers

These questions & answers about blockage of roof venting intake at the eaves or soffits were posted originally at SOFFIT INTAKE VENT BLOCKED - be sure to review the guidelines and suggestions found there.

The photograph at page top shows an attic whose intake venting is blocked by fiberglass insulation.

[Click to enlarge any image]

On 2018-09-17 by (mod) - is it ok to deliberately block soffit intake vents?

Charlie

You raise a good point: whether or not we have a moisture or mold problem under a roof, in an attic, or in a cathedral ceiling that is not vented or whose venting is blocked depends on a number of site variables such as climate, sun exposure, wind direction, and indoor air leaks and moisture sources that send moisture into the roof cavity.

Even if there is not always a mold problem with blocked soffits (and often there IS a mold problem) blocked soffit intake vents, especially if combined with the presence of air movement OUT of the roof space (through leaks or through a ridge vent or gable end vents) is likely to increase the heating and cooling costs for the building by sucking conditioned air out of the structure.

On 2019-01-23 by Charlie

It's interesting to see in a post that the soffit vent blocked with mineral wool insulation did not cause mold problems. I have a Freezing Room Over Garage and am considering blocking the soffit vents with rock wool to reduce the air flow into the rafters and wall cavity behind the insulated knee wall. Since rock wool allows moisture to pass through, I am wondering if it's ok to use it to block the soffit vents.

On 2018-09-17 by (mod) - signs of roof failure blamed on inadequate roof ventilation

I and others would need to know more details about how your house is constructed to offer useful opinion about solving the venting problem.

However it might be useful to understand that a hip bridge which provides an exhaust outlet for air isn't going to help you with Rafters that don't originated at an Eaves or overhang.

The classic example of this problem is with Valley Rafters that don't have an opportunity for an air Inlet. It probably would have been a better designed to go to a hot roof.

On 2018-09-16 by Curt Hardy

We expanded our hip roof with an attic residence 13 years ago. The contractor gave us the opportunity to vault the ceilings in the added space, and we agreed.

We are now seeing signs of premature roof failure and realize that part of the vaulted area vents into the original attic space, and part of it does not reach the original attic, and stops at the hip ridge rafters.

The ceiling is constructed with baffles plus R30 batt insulation.

A roofing repair contractor has suggested trying a hip ridge vent along the hip ridges to provide an exhaust point for the rafter bays that cannot reach the original attic space.

Is this possible ? We are desperately trying to avoid tearing out the ceilings and converting to a closed cell spray insulated "hot roof".
Please help !

On 2018-06-16 by Patricia wood

We have both blown and rolled insulation in our attic. If there is the blown insulation in the eves, can it be blown out of the eves from the outside? We just had the roof replaced. They installed two new ridge vents. Is there a problem with the loose tar gravel lying on the insulation?

On 2018-04-22 by (mod) - soffit vent openings are clogged

David

Look for a local siding or general contractor who can open the soffits by removing the eaves covering from outside to remove the insulation - taking care to keep insulation over the outer wall top plates. You may need the contractor to add baffles as we discuss above.

Sometimes it's easier to work from within the attic - particularly if the roof is steep slope giving good access to the house eaves.

On 2018-04-22 by David Cupp

30 soffet vents in overhang. Most are clogged by one sided kraft fiberglass batting. Have been for iver 30 years.

Can’t clear myself as in now 77. Wish I’d found this out long ago. Found mold in A/C plenum last week as ducts were to be cleaned. Have new plenum and ducts. Need to open soffers to help ventilate attic and keep mold out. Need some help

On 2017-09-01 by (mod) - honeycomb soffit vent openings painted shut

Steve,

If just a few holes are closed that's probably not a concern, but I can't know from just your text how much venting is blocked. You are welcome to use the page bottom CONTACT link to send a photo or two showing the situation and we can comment further.

Also you could probably easily open the painted-over holes by probing with a suitably-sized tool like an awl or a tiny screwdriver.

On 2017-09-01 by Steve

I have continuous honeycomb 2 inch wide soffit vent around all edge of the roof. we had painter to pain the house, unfortunately, the painter painted the soffit vent. but only some spots with paint covered. most places the hole are still open. Will this cause any problems ? thank you!

On 2017-09-01 by (mod) - will a little bit of paint block the soffit intake vents?

Steve,

The photograph at left shows a partial blockage of eaves or soffit intake venting by paint, discussed just below.

If just a few holes are closed that's probably not a concern, but I can't know from just your text how much venting is blocked. You are welcome to use the page bottom CONTACT link to send a photo or two showing the situation and we can comment further.

Also you could probably easily open the painted-over holes by probing with a suitably-sized tool like an awl or a tiny screwdriver.

With benefit of having now see your photos and having zoomed-in (photo above) we can see that in a few areas the soffit intake vent screen openings were indeed blocked by your painter's blobbed-on brush application.

For most of the roof eaves you've probably lost 10-15% of intake airflow.

IF you see signs in the attic of a history of inadequate under-roof venitlation (mold, moisture condensation, moisture damage not from roof leaks)

THEN it would we'd be justified in suggesting that the blocked vent strips should be replaced. That's assuming as well that there is an un-blocked, effective, continuous outlet vent at the ridge.

My photo (below) shows a close-up of effective, un-clogged perforated soffit vent strip openings.

Otherwise the only remaining concern would be if the thickly-applied paint blocks virtually all of the air inflow between individual pairs of rafters - you can check this from the attic interior by seeing where light is blocked or not down in the house eaves or soffit.

If you find rafter bays blocked entirely of incoming air it would be worth a bit of jabbing with a suitably sized tool to open the clogged vent openings.

If you live in a fire-prone zone such as some California areas, then I'd consider replacing the existing soffit intake vent strips with a product like those described

at ROOF VENTILATION, FIRE RESISTANT.

Watch out: the greatest risk of a soffit venting project is the injuries that would ensue if you or your painter, returned to fix his work, fell off of the ladder or scaffolding.

On 2017-09-01 by Steve

I have continuous honeycomb 2 inch wide soffit vent around all edge of the roof. we had painter to pain the house, unfortunately, the painter painted the soffit vent. but only some spots with paint covered. most places the hole are still open. Will this cause any problems ? thank you!

On 2017-05-09 by (mod) - Paint should not be allowed to block or clog up the soffit vents

Deb

Paint should not block or clog up the soffit vents or you'll cut off the attic venting.

Usually the soffit openings are large enough that rolling on or even light spraying of paint won't close off the venting.

On 2017-05-09 by Deborah

My husband think ,he will paint over all the metal sofit on roof edge..covering all holes ,I don't think he should do this,correct?

On 2016-10-08 by Linda

I meant to say plugged up, not pulled up.

If you paint the soffitts and they get pulled up, what can happen to your attic insulation?

On 2016-09-14 by (mod) - where should attic insulation go: into the soffits?

Justin,

Please take a look

at SOFFIT INTAKE VENT BLOCKED

to be sure that you understand the disadvantages of having an attic that does not have working ventilation. If you decide you want to make your attic have working ventilation and you do not want to block the sockets with insulation.

There may be other serious fire hazards as well if you were recovering electrical components, recessed lights, or a metal chimney.

On 2016-09-10 by Insulating old attic that has the old wood soffit

Hi, I'm on a budget and re-insulating my attic with atticat blow-in insulation

The attic is basically a crawl space and there is venting in the gable ends and a few whirlybirds on the roof...
If I'm blowing the insulation do I just box around the vents on the gable ends, or do you not insulate at all on top of the soffits even though they are plywood .

I would lean towards not insulating the soffits at all but have heard differing opinions.

Also going around a wood fireplace exhaust pipe... Would I have to build something to keep the insulation from making contact with that, or is it built to handle the heat ...

Thanks
Justin

On 2016-08-15 by (mod) - is it ok to close off eve vents in garage and or put gable fan to pull air out.

You can close off your attic roof venting system, under the theory that there is no heat source in this space so ice-damming ought not be much of a problem (Jersey shore is also a snow-area, right?)

However in my OPINION in summer the roof will be hotter than if it had continuous soffit intake and ridge outlet venting, thus perhaps reducing the shingle life.

A gable-end vent is not effective in an attached garage and if there are ridge and soffit venting installed the gable vent can become a short circuit feeding air to the ridge vent so reducing air movement in at the soffits or eaves: the result is that the lower roof areas and roof areas closer to the house common wall are not vented.

Same problem with a single power vent.
If you see moisture accumulating in the garage - roof stains, mold, that'll up the priority of drying out the space.

On 2016-08-15 by Alan

I have a attached garage there's no ceiling,just another level for storage.the previous owner put a vent in wall of garage.so I guess this acts as a gable vent for the house.

There is also a gable vent in the garage is a gable close the rest of house has insulation , vented soffits the roof has a actic fan .

I closed off the soffit vents in garage so it stays a little warmer for the winter there's no heat in the garage.I know it's hotter in the garage in the summer with no real air moving,so maybe I can also put a gable fan in the garage

Question is is it ok to close off eve vents in garage and or put gable fan to pull air out. I leave in new Jersey near the shore.
Thank you alan

On 2016-05-15 by (mod) - response to potential wild fires burning through soffit vent and igniting the attic

Thanks Anon. You are noting something important.

Chapter 7A of the California Building Code recommends soffit vents designed to resist the intrusion of embers during a forest fire.

Excerpting from the source given below

Chapter 7A vent requirements:

Chapter 7A says that vents must resist the intrusion of embers and flames, or that they shall be protected by corrosion resistant noncombustible wire mesh screen with openings.

1/8" mesh is also allowed. Vent designs that incorporate plastic components would not comply with the noncombustible wire mesh screen language in Chapter 7A.

Chapter 7A language also specifies that vents cannot be used in an eave application unless that vent has been shown to resist the intrusion of embers and flame.

Although there are a now few vents that have been accepted for use by the California OSFM, a design that incorporates two sets of through roof vents, one set for inlet air located near the roof edge, and another for outlet air located near the ridge (as shown here), has been used.

Modifications to Chapter 7A that would provide for more prescriptive measures for complying are currently being considered by the California Building Standards Commission.

Currently there isn't an accepted procedure to evaluate ember intrusion, but an American Society for Testing and Materials (ASTM) task group is currently developing a standard test procedure.

- see http://firecenter.berkeley.edu/bwmg/vents-2.html

On 2016-05-15 01:00:04.298645 by Anon

In response to Charlie regarding California automatic soffit vent closure.

I stumbled across a company product called Vulcan Vent. Perhaps the recommendation is in response to potential wild fires burning through soffit vent and igniting the attic? Good luck on the rebuild!

On 2016-02-18 22:50:10.602657 by (mod) -

George

we need to investigate this further (really "we" means don't feel alone while you do all the work)

FOAM seeping thru soffits suggests that this may be a HOT ROOF design - if that's the case there is no venting. Instead the space between rafters is completely filled with foam. Search InspectApedia

for HOT ROOF DESIGN PROBLEMS to read details.

On 2016-02-18 by George

Hello - I am in the process of buying a new construction home and just had the inspection.

The inspector suggested that the soffit's were installed incorrectly and additionally, the foam installation was seeping through the soffit vents. Is this a big deal in regards to possibly developing ice dams etc? I live in the North East so it is a concern of mine. TY!!!

On 2015-12-29 7 by (mod) - roofer says insulation was blown into and blocks my soffit vents

Why are we removing the blown-in insulation: due to blockage?

If so I'd consider installing soffit vent baffles to insure that there is a good air intake path while at the same time avoiding creating a cold spot at the ceilings near the exterior walls. Insulation conractors or any handyman can do the job.

On 2015-12-29 by Anamandy

I was told by a roofer who inspected the attic for leaks from my slate roof that my soffits were full of blown in cellulose insulation and that it had to be removed. He said I had plenty of soffit vents which he viewed outside and felt.

He then told me he didn't do that work and I'd have to get someone else to do it. He wouldn't recommend anyone to me either. Said he lost customers before by recommending people who his customers wound up not happy with and didn't want to do so now.

My questions are what type of business do I look for to do the work and is it just a question of sucking out the insulation with a shop vac?

On 2015-11-26 by (mod) - fire-stopping soffit vents: automatic soffit vent closing system to protect homes from fires in Northern California?

Charlie

Indeed there are self-closing eaves vents or soffit vent products that reduce the chances of fire-embers moving up into a building attic through the eaves vents.

[Click to enlarge any image] Shown here, excerpts from the Caruso Hendricks Ember and Fire Resistant Vent patent (2007).

Watch out: before buying and installing self-closing eaves vents or soffit vents for fire protection you should check with your local fire inspector for suggestions and to learn what systems are approved were you live.

A detailed answer to your question along with a description of both soffit and ridge vents that are "self-closing" to reduce the ability of embers to enter a building soffit, eave, or roof cavity (at the ridge) is at

ROOF VENTILATION, FIRE RESISTANT

On 2015-11-24 by Charlie Hart

We lost our home recently to a fire in northern CA and have to rebuild from dirt.

I was told that we might have to install some sort of automatic soffit vent closing system that closes off when it senses heat from a fire.

I've tried looking at the 2013 CA Fire codes and did not see anything like that there. Have you heard of such a thing and if so where can I find more information on it?

On 2015-09-24 by (mod) - are round 2" soffit vents sufficient intake area?

Thanks for the question, Jim.

My opinion is that NO spacing would be appropriate for 2" round vents since that approach to soffit intake venting is inadequate because the volume of air intake at the building eaves will be inadequate.

What works best is a continuous soffit intake vent strip running the entire breadth of the building.

On 2015-09-24 by jim burns

In a 24" soffit,framed 24" oc.what is the appropriate spacing for 2" round vents?

On 2015-05-25 by Anonymous

Having read your helpful article on the importance of soffit intake venting, but wanting to avoid aluminum soffits, could a possible decorative solution be to run lengths of pine parallel to the roof as soffits with screen mesh stapled to their back allowing for a 1/2" gap between the wood for air flow?

...

Continue reading at SOFFIT INTAKE VENT BLOCKED or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Roof Soffit Venting Articles

• ATTIC CONDENSATION CAUSE & CURE
• CATHEDRAL CEILING VENTILATION
• PROBLEMS with PARTIAL ROOF VENTILATION
• ROOF VENT SOFFIT + RIDGE NEEDED
• ROOF VENTILATION NEEDED?
• ROOF VENTILATION SPECIFICATIONS - home
• ROOF VENTILATION, FIRE RESISTANT
• SOFFIT INTAKE VENT BLOCKED
• SOFFIT INTAKE VENT INSPECTION
• SOFFIT VENTILATION SPECS

Suggested citation for this web page

SOFFIT INTAKE VENT BLOCKAGE FAQs-2 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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