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Attic venting blocked by fiberglassBlocked Soffit Intake Vent Effect FAQs
Q&A on Causes of Condensation, Ice Dam Leaks & Mold in roof cavities & attics

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Blocked or inadequate roof ventilation air intake opening questins & answers:

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.

We also explain that attic or roof exit venting without adequate soffit intake venting increases building heating cost.



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This article series describes 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.

Blocked Soffit Vent Intake Questions & Answers

Soffit intake vent openings partially blocked by paint (C) InspectApedia.com S-FLThese questions & answers about blockage of roof venting intake at the eaves or soffits were posted originally at SOFFIT INTAKE VENT BLOCKED

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

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

[Click to enlarge any image]

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

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.

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.

Perforated soffit intake venting strip opening dimensions (C) Daniel Friedman

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 DESIGNS: UN-VENTED ROOF SOLUTIONS 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?

Fire and ember resistant soffit vent, Caruso Hendricks Patent US20080220714A1 at InspectApedia.comCharlie

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?

Question: soffits are covered with insulation, how do I get venting intake?

(May 30, 2014) Re-posting comment from Anonymous on 5/29/14 without his caps-lock on

My roofer wants to cut into decking a small area here and there along gutter line because my soffits are covered in attic with insulation. Is this a good method? Doesn't it leave some shingling hanging without support? Concerned.

Other than that, he said smart vents are dumb vents except in the south bc they can cause ice damming in winter in gutters and back up that ice into shingled areas. Other than that there are baffles which seem ok. I like his idea, but cant find it on internet.

Reply:

Anon I don't quite have a clear idea what's going on, but if by "decking" you mean the roof deck, I think you are talking about looking for a way to get intake ventilation into the attic.

The best solution is to bring insulation out over the wall top plate and at the same time keep it off of the underside of the roof deck and give an air path by inserting baffles (carboard or styrofoam) sold for that purpose, between every rafter pair - work done from in the attic.

Then either go to a perforated soffit cover or cut a vent opening continuous along the soffit to accept a perforated vent strip.

We do agree with roof deck removal as an intake port along the entire lower roof edge just for the case of roofs built with no roof overhang at all. IN this case a Hicks Starter vent or equivalent is added to support the shingles while providing a (modest) intake vent opening.

Watch out: even adding a starter vent and cutting off roof decking for a couple of inches won't work if the space inside is filled with insulation. So you're back to inserting baffles, which means there was no reason to cut roof deck in the first place.

Question:

(July 31, 2014) Rick said:

Question....I have trying for several years now to fix the heating and air condition in my house. Its 11 years old 4 bd coloniai and we live in the PHilladelphia area. We have air seal the attic added an R60, which is great but the company did not install or install baffles correctly.

So, now I have No ventilation in there. They pushed the baffles so far down that they were blcoking the soffit. I went up there and actually installed AIR VENT Baffles. However, I cannot get to every part of my attic. I need about 10 more bays to hit.

It gets very hot up there and cold during night., which causeses humidty. Also, I do not feel the air coming up through all baffles??? By not having them all cleared, will that limit air flow in others? I do not know how I can reach the other eves to clear blockage and install correctly. Also had a new ridge vent installed. Pleas advise

Reply:

Rick,

Opening additional soffit vents that are blocked should not at all reduce the benefit of the ones that are already open.

For soffits that we can't reach from within an attic another approach is to work from a ladder or scaffolding from outside, removing the soffit covering, making necessary clearance openings, then replacing the covering.

Don't forget to provide good exit venting at the ridge.

Question: do I need to add soffit vents or can I just add more insulation in the attic?

(Nov 3, 2014) Glenn said:

Hi, I have a colonial with an overhang in Baltimore MD. The soffit looks to be unvented as I see no light coming through ( after moving back the insulation) and there are no ventilation panels covering the soffits, only solid panels.

Insulation in the attic is all the way back to the roof. I do have triangular openings at each end of the house at the top of the peak, a ridge vent and a solar fan. No indication of any mildew or other problems other than one ice dam years ago after a blizzard.

Do you think I should have a contractor take down the panels covering the soffits, cut a continuous vent, pull the insulation back and have vents put in? Or do you think I'm ok to just have additional insulation put in the attic ( which is what started me down this path in the first place).

Thanks for the advice on your website and any specific guidance you can provide me.
Glenn

Reply:

Adding insulation won't make matters worse but will make installing baffles to permiypt venting much more trouble later. Do it now while it's easy.

Your ridge and gable end vents will never cool nor dry lower roof areas. I'd install baffles, soffit ending, and then close of the gable end vents to stop that air short circuit.

Question: roof venting schemes for Winnipeg

(Dec 8, 2014) Linda Hegg said:

Winnipeg, MB, Canada: MY house has drastically changed from low humidity to high humidity after fiberglass loose attic insulation was added from R20 to R50 on Oct 22,2014. After 10 years, all of a sudden (started 3 1/2 weeks ago when the cold weather hit), we have sweating windows that cannot be wiped dry, pooling water on sills and black mould growing on walls, baseboards, all window sills, etc.

Before there was no insulation at the edges of the attic (over the soffits), now they all covered up with fiberglass insulation. Would that enough to change the environment of the house so much from low humidity to high humidity?

Reply:

Linda

Adding fiberghlass loose fill itself should not change humidity in the space below, though you might have slowed air leaks up into the attic and thus changed the house air movement pattern.

I'd look for

1. unsafe gas appliance venting - producing moisture and dangerous carbon monoxide

2. a moisture source in the building

3. poor insulation installation that blocked attic venting

Also see

inspectapedia.com/sickhouse/Humidity_Level_Target.php

and see these

Moisture Diagnosis & Cure Articles

 

Question: replacing aluminum soffit vents with vinyl reduces the actual vent opening area - seeing attic mold

7/8/14 Richard said:

Three years ago, I had my 34x24 hip roofed house have its roof and soffit vents replaced. The original ridge was continuous aluminum vent and so was the original soffit vents. The new soffit vents are vinyl and continuous but are only 3.5 to 4 inches wide.

When the contractor originally replaced the soffit vents I expressed concern that just looking at the vinyl soffit vents would provide much less air into the attic. The contractor assured me it would be enough [ventilation in the attic] but now I've noticed mold in the attic. And some limited amount of water had puddled on some boxes under the ridge.

So then I started looking at calculations.

  1. I estimated that the 1" aluminum continuous soffit vent originally on the house was providing 545 sq-in of net free air(NFA).
  2. I estimated the original 1" aluminum at the ridge was providing about 150 sq-in NFA.
  3. The new ridge vent is providing about the same as the old vent,
  4. But I think the vinyl soffit vents are now only providing 232 sq-in NFA.

I live in NH- Do I need adjustments of both ridge and soffit?

I have a concern that the water on the boxes was an indication that the soffit venting was insufficient.
The original seemed to be close to the 1/150 rule. But the new design does not even meet the 1/300 rule because the ridge is only about 3/4 that needed for a 34x24 attic.

Are the any rules of thumb that contractors should be using when replacing aluminum vents with vinyl ones?

Reply:

Richard,

Thanks for the interesting and important analysis. Indeed some contractors are not into reading instructions, building journals etc. We joke that the instructions are just used to kneel upon while doing the actual work.

Rule of thumb for venting a standard gable roof, soffit to ridge ratio: Basically we want the soffit intake to be 2x the outlet vent opening. Indeed the smaller perforations in some soffit vent coverings can have the effect you describe.

Some hip roofs add a spot vent on the smaller triangle hip roof ends at the triangular apex near the end of the ridge to add exit opening. I'd consider that improvement if we also need more hip roof exit venting for a hip roof design.

...


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