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.

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

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]

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.

See details at ROOF VENT if NO SOFFIT

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: I do not feel the air coming up through the roof soffit vent baffles

(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 HUMIDITY LEVEL TARGET

and see these moisture diagnosis and cure articles listed at the end of this article.

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.

On 2012-12-20 by Lee Mitchell

I have recently purchased a new house and we have condensation that bad that the insulation is soaking and that the bedroom ceilings have started to leak.

The air vents in the soffits have been fitted directly behind the guttering.

The building contractors ahve put an additional vent within the roof but with no effect.

The roof vents are in one vertical line one above the other and not spaced out across the roof. The building contractors have also tried to use a de humidifier but this doesnt seem to make much difference.

I have asked the building guy if the insulation is vlocking the vents and he has said no. The roof is lined with felt which is not of the new breathable material. Please can anyone help me as this is beginning to do my head in.

On 2012-06-26 by (mod) - /ventilation/Soffit-Vents-Blocked-FAQs.php

Anon:

"Testing" is not usually peformed on soffit and ridge venting - rather we start with a visual inspection to see what is present, look for blockages, and if appropriate, to determine the total amount of intake (soffit) and outlet (ridge) venting.

I have done some air movement tests using smoke generators, and I have measured changes in attic air temperature when we cut in ridge and soffit venting.

But that's not measuring air movement from outside up through the roof and out again, nor measuring air leaks from the building interior if the venting in the roof isn't properly balanced.

Even "testing" such as by using some variation of a blower door test on the attic would not be technically exhaustive, as actual air movement and thus ventilation varies considerably based on other factors such as wind directions, time of year - indoor and outdoor temperature differences, and operating of heating or cooling equipment in the building, and of course, on insulation and air leaks.

Asphalt shingles that ever sealed over many years may have been improperly installed or may have had defective glue strips.

About the roof vent fan, removing it should not hurt you if the intake and outlet passive venting openings are adequate and unblocked - and the passive venting approach has the advantages of

- operation without electricity

- operating year round, not just when the fan runs

- providing drying ventilation across all under roof surfaces rather than concentrating it around the fan area

On 2012-06-26 by Anonymous

Is there a simple way to test a soffit and ridge vent system? We have a T-shaped ranch with a new metal shingle ( Futureroof Slate ) roof. We insisted that the asphalt shingles be removed even though " they " say that metal can be installed on top of them.

The 19 year old shingles NEVER SEALED and simply lifted off! The felt was in perfect condition but we still covered it with a synthetic ( Robetex 300 ) membrane. Two years ago I had the attic floor reinsulated with open-cell foam and the guys were careful to install baffles to keep the soffit vents open.

I can see light through all of them.

We were advised to remove an attic roof fan as it would supposedly counter the soffit and ridge system.

I have been monitoring the attic temperature and find it to be around 20-25 degrees warmer than the outside air during the hottest part of the day.

After sundown, the attic temperature drops fairly quickly. Is this temperature difference what we should expect? Should I NOT have removed the roof fan?
Thanks in advance.
Russell

On 2012-06-26 by (mod) - adding a roof vent fan without soffit intake will suck air out of the occupied building space

Bob, adding a roof vent fan without soffit intake will suck air out of the occupied building space when the fan is running, potentially increasing building heating or cooling costs; and it is likely to vent and dry unevenly under the roof surface.

Unblocking wood-blocked soffits is labor intensive - I've done it - we either remove the blocking entirely or cut most of it away, followed by providing soffit intake venting and using baffles as needed to avoid blocking the openings with insulation.

On 2012-02-07 by Bob P.

I have a house with a hip roof and ridge vent. Had additional blown-in insulation added and have moisture problem.

Discovered that my soffit is completely blocked by wood. Understand that best resolution is having continous soffit vents added, but because of expense and the difficulty in pulling back insulation and adding baffles (low attic access and compacting insulation)could adding roof intake vents fairly low work as a substitute?

Or even blocking the ridge vent and adding a power ventilation fan and roof intake vents? Roof was put on about 15 years ago and shingles are showing wear.

On 2011-10-29 by Bob Schneider

Thanks for comments about soffit vents and baffles. Looking for additional guidance on the custom baffles and need a sound sealing approach for the gutter board/underside of roof junction.

My 1st letter was a bit vague so here is a bit more explanation: My roof with drip edge extends about 3 inches over gutter board. Inspection of the area revealed a wood moulding which was covering a 3/4 inch gap between the underside of roof deck and gutter board.

This was rotted away exposing the attic insulation to the elements along most of my roof line.

My goal was to seal up that gap by replacing the moulding with a custom L shaped strip of metal flashing, then sealing and screwing it to the gutter board and tucking snugly to underside of roof deck.

The new sealed & screwed flashing/moulding extends only 1 to 1-1/4 from gutter board - so it is well protected by the overhanging drip edge

. I didn't want a gap to allow ice especially to travel up and under and into house via the soffits so I thought sealing would provide additional benefit. Thoughts on this?

The baffles now in early construction phase are time consuming but provide a additional R19.5 from top plate 4 feet up roof deck while a 1-1/2 inch baffle allows that outside air to keep the roof deck as cold as possible and hopefully minimizing the ice damming which had gotten worse in recent 4-5 years (likely from those rotting mouldings described above!)

On 2011-10-16 by (mod) - 1 or 2" round louvered vents are never adequate ventilation

Bob,

Round roof vents such as those 1 or 2" round louvered vents are never adequate at one per rafter bay.

Cut a continuous vent strip and cover it with perforated soffit vent strip material. Or remove the soffit covering, open any blockages, insert your baffles from outside if that's easier, and install perforated soffit covering.

You can make baffles but you can also buy ready-made roof soffit vent baffles that are inexpensive and should work

I don't recommend your sealing approach - sealing roof decking from underside invites continued wetting and ultimately rotting of the roof sheathing from above.

On 2011-10-15 by Bob Schneider

I have a few comments about roof ventilation on my 1925 colonial. I currently have non functioning ventilation system.

The GOOD- a ridge vent and smaller round soffits installed 10 y ago.

The BAD- insulation never removed from soffit and painter sealing over the soffit vents with paint. Ice damming and deterioration of top edge of gutter board allowing water to flow back into soffit and lead to damage and paint peel have resulted.

My solution:

1) I am going to install new round soffit vents to allow the prescribed amount of NVFA intake air to match the ridge vent NVFA.

2) I am going to construct baffles with blue poly iso board to a depth of 3-1/2 inches (roughly R19) extending for 4 fee top of wall.

3) place flashing with sealant at gutter board and underside of roof deck to prevent the ice and water from flowing back into the house.

4) repaint the house

Questions I have revolve around:

1) Is DOW TUFF R adequate? I plan to sandwich 2 pieces together with foil facing up on the top piece.

2) are the round vents probematic at all? I have found what i believe to be a good source and as a homeowner think I can handle a hole saw vs. a circular saw upsidedown.

On 2011-10-13 by (mod) - remove insulation blocking soffit air intake in the attic: how-to

Gil,

We clear insulation that blocks the soffit air intake from inside the attic, manually, by hand, wearing appropriate respirator and tyvek overalls

. If you have no access to the attic space you'd have to work from outside - a more involved procedure: remove the soffit covering, push or remove insulation to provide an air path or insert baffles from that side, and replace the soffit covering.

Obviously the latter is a lot more work.

Don't pull back insulation so far as to leave cold ceiling spaces, just clear it back to the top plate and insert a baffle if necessary to hold the opening clear.

On 2011-10-11 Gil

Correction. That was loose-fill fiberglass insulation not mineral wool.

On 2011-10-09 18:13:41.224934 by Gil

My baffles are blocked my mineral wool insulation. They are clear at the soffit side and the attic side but light does not shine through, not even a flashlight, so the blockage is inside the baffle. How do you clear that?

On 2011-09-14 by (mod) - no place for a ridge vent.

Steve, if the hip roof is a pyramid style there is no place for a ridge vent. Or if the horizontal ridge is just a few feet it will br inadequate for ridge venting. In that roof design we use spot vents or turbine vents near the peak for exit venting.

On 2011-09-14 13:36:34.629786 by Steve S.

I have seen mention of not using ridge vents on hip style roofs. Can you explain if this has any basis to it or not?

On 2011-09-14 by Steve S.

What is the possible downside, if any,to entirely removing the wood soffit panel but not increasing the rooftop vents? There would now be more than twice the amount of vent opening at the soffit than at the rooftop.

On 2011-09-11 by Fred Hamel - roof temperature measurement report

I live in Canada. My house was built in 1963. As you mentioned, in those days the soffit were made of plywood without any sort of venting.

Later aluminum soffit were added over the plywood. And then soffit vents were added by piercing a whole trough the aluminum and the plywood.

I wonder if my roof gets enough ventilation. I just recorded the following temperature today:

Outdoor: 21 celsius or 68F

Indoor: 25 celsius or 77F

Inside my roof: 36.7 celsius or 98F

Does this temperature difference indicate a poor ventilation?

On 2011-08-11 by (mod) - faux soffit vents around the house.

Ava I'd like to see a photo of just what you're talking about - see the CONTACT link at page top, left, or bottom.

But if you have what I suspect, it is very tough to get attic venting in on older, often pre-1900 homes through roof eaves that incorporate an eaves trough gutter. Not only is that whole structure in the way, but often there is solid wood framing at the wall top - no easy openings for airflow.

To be sure we're on the same page I need to see outdoor and indoor attic photos of the house eaves or at least some sketches. You may have to eschew venting and rely on ice and water shield membranes at roof edges and other, less effective attic vent measures.

Watch out: don't add just ridge vents if there is no intake venting - you'll just increase building winter heating costs.

On 2011-08-11 by Ava

I have faux soffit vents around the house. There is no ventilation getting into the attic and creating vents through the attic is impossible due to the angle of the roof. Is there any way that vents can be created without removing the whole eavestrough system?

On 2011-08-08 20:46:45.662249 by (mod) - eaves are blocked by mineral wool insulation.

Steve, the answer depends on ease of access. In a high attic with plenty of room to access the house eaves we rake back or even shop-vac out the insulation where it's blocking the eaves.

I prefer this approach if it's possible as we can be dead sure we are leaving insulation all the way out over the top of the wall (avoiding ice dams) and it's easiest to install airflow baffles between each rafter pair from this position, and finally because we can inspect the whole attic/under-roof insulation system for quantity and uniformity, correcting as needed.

If there is no easy access to the building eaves from an attic inside, we work from outside by removing the soffit covering, removing just enough insulation to give air path, inserting baffles as needed, and then perforated soffit covering.

On 2011-08-08 by Steve

My eaves are blocked by mineral wool insulation.

What is the best way to remove the insulation.
Thanks in advance for your help.
Steve Ritz

...

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 SOFFIT INTAKE VENT BLOCKAGE FAQs-2 - more recent questions & answers about the cause, effects, and cures of blocked soffit intake venting on roofs

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

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