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Roof venting on colonial with no soffit

7166 Views 22 Replies 5 Participants Last post by  scottonline
I have a colonial style house built in 1960. It does have a ridge vent. The house does have soffit, but it is packed with insulation that is almost impossible to remove due to shape of roof (see image).

Only one side is open to add a gable vent. Would one gable vent help in this situation? Maybe with a power fan? It appears there was a gabble vent in the past, but on the previous remodel it was replaced with the ridge vent. Likely when the mold growth started.

The attic has R 40+ insulation.

The roof sheeting has mold growth. Before I take care of the mold I need to correct the venting.

More photos in post #5


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Is there no baffle in those low slope regions that goes to the soffit?

A picture from the exterior would help and anytime we see mold growth, there is something critically flawed with the build envelope as well.

What does the ceiling look like and how many penetrations are in it? Relative Humidity level in the house?
Can you install gable end vents in your attic? Couple of those (one at each end of the house) will vent some air.

Are the cells between the rafters packed with insulation from the top of the drywall right up to the roof sheathing?

Where is the mold located, on the top or bottom of the sheathing, and is it throughout the entire roof or just in spots (For instance where you had leaks)
Here are pictures of the outside roof and the inside. One picture shows where I attempted to pull the insulation back, but it is basically impossible to get to the location since it is only several inches high. Then at that point it starts its slant down to the soffit over (see image in first post)

The humidity on the inside is 45% at the highest in the basement. I think the main issue was the previous owner used a humidifier. Now I believe the moisture is corrected.


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Moisture might be corrected but anything to too high without venting.

You need to pull that cellulose back and see if there was a vent chute installed in those cathedral sections. It needs to be cleared out and allow the soffits to vent to the attic.

You should not have a vapor barrier on the insulation and certainly not towards the cold (Attic) side of the equation.

Pull the insulation back from those areas where there should be a vent and let us know what you find.

You attic will continue to mold if you do not correct these problems and cellulose is not well suited for a dense pack/hot roof deck.
Moisture in attack

Photo four shows a rectangular piece of ductwork extending into the attic in the lower left quadrant of the photo. What is that for? The photo also shows what appears to be a cut out for a gable end vent that has been covered with plywood. Install louvered gable end vents in both ends of this roof area, and extend that ductwork out of the roof if it is a bathroom vent. I suspect it might be a dryer vent, and that would explain all the black mold on the woodwork. Once you do the above, spray that black mold with a 3/1 mixture of bleach and water with a sprayer that really atomizes the mixture. Protect your eyes and lungs.

I can honestly tell you that there are many many houses that have had insulation shoved up against the roof deck between the end of the collar beam and the top of the interior wall cripple studs when the upstairs was finished in colonial and cape cod houses, and they do not have the problems you have. You are dumping hot, humid air into this space from somewhere. Start with the most obvious and simple things first and see if that solves the problem.
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Further review

I looked a little closer at your photos and it appears that you have no ridge vent. The Framer held back the sheathing to allow for one, but it was apparently never installed. Your question regarding gable end venting is that you need a vent in both ends to do any good. You need cross ventilation. Another gable end vent and stopping hot air flow into the attic will probably solve your problems.

Dont worry about the insulation up against the deck or the clogged eaves yet. DO the easy, cheap stuff first.

I could go into a long dissertation about ventilation vis-a-vis the effect on the roof system, but that is another issue, most of which is pure unmitigated Bovine Scatology that was perpetrated by the shingle manufacturers to cover the fact that in the late 70's they were manufacturing products that were not capable of dealing with the environment into which they were being placed. It had to do with fiberglass reinforcing matts and the oil shortage.
There is a ridge vent just difficult to see in the pictures. The metal duct I believe is for the bathroom fans. I will check though. The dryer vents out the wall in pic 2.

With the gable vents will I want to install them at the highest point or just above the insulation? What will work best with the ridge vent.
Bathroom Fans

And you have a teenager that takes long hot showers? Just guessing. You need to vent those bathrooms up through the roof. I dont know why you have a rectangular duct from the bathroom fans, maybe they are tied together. You are better off running two separate 4 inch PVC vents up through the attic, that way you can use a typical pipe flashing with a rubber stretch collar. You do have to remove shingles and properly install the roof jacks. Glue a return bend or make one up with two street els so the vent will point back down toward the roof, or just install an aluminum flue cap on the top of the pipe. Extend the vent up high enough to clear any anticipated snow. Run the pipe laterally to the back of the house and
go up through the deck with clearance around the pipe. You can paint the pipe with plastic paint to match the roof, and support the pipe with 1/4 inch U bolts, or plumbers strapping.

The gable end vent should be installed at the very top of the gable with the top flange under the rake board if possible. you will need some J channel to trim out your siding, and maybe some pre primed 1 x 4 pine.
Always make sure that components are shingling water, and if you use sealant buy the best algae resistant Silicone you can get. Forget Latex, you dont want to get back up there too often. Wipe with alcohol before application, and tool with spatula.
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Thanks Jagans I will get this done as soon as the weather will allow.
Good Luck

Good Luck Scott, Tie your ladder off, and be careful up there. Let me know if you need a vent stack detail and I will find one for you.
It doesn't appear the bath fan rectangular ducting is depositing the moisture/mold in your attic. The picture shows the site-built truss struts clean, unlike the other end of the attic. Another pic of the worst cavities from 6' away would help us. Where does most of the moldy area above, lead to below? A wiring/plumbing hole in the top plate from below, even an air-path to the basement/crawl? You are getting extensive air/moisture from below, up the sheathing (near the rake in the pic.) due to the stack effect, and possibly lack of enough attic ventilation; Did they miss a major hole when air sealing? Did they air seal the basement/crawl wiring/plumbing holes in the floor sheathing? Did you pull more cellulose from the area to check--- after the picture?
I see mold all the way down the top chords (rafters). Is there cellulose in the lower sloped ceiling (cathedral) and it is NOT vented with baffles:

It doesn't appear the bath fan rectangular ducting is depositing the moisture/mold in your attic.
The entire attic has similar amounts of mold on the sheeting and trusts. However the mold is only growing on the North side of the trusts and not the south that is why one end appears clean in the picture.
The South side will remain warmer via exposure and have a higher dew point.

All the above suggestions are spot on (Air Seal, vent, get moisture out of the home, etc).
Mold Location

Hot moist air will disperse very rapidly throughout the attic, it does not stay on one end. We are talking about pressure here, and the temperature will constantly attempt to reach equilibrium. I suspect that what WOW says is correct. There is just enough of a difference on the north end to create the conditions you have. You may very well have hot air coming from somewhere else, considering the fact that someone dumped your bathroom vent into the attic. I am pretty darn sure that gable end venting will solve your problem, Scott. I had a home in North Jersey in which they dumped the bathroom vents into the attic. It had gable end venting, and never had a mold problem, but I had to install through roof venting due to a whole house inspection when I sold it.

PS They are Trusses, not trusts
I hope I'm wrong and just venting the bath fans outside solves your problems.

I hope I'm wrong and just venting the bath fans outside solves your problems.


That is certainly the first thing that I would do to start with.
I agree, that goes without saying. I usually site the Code requirements for bath venting but find it unnecessary as more members have read them from me here over the past 4 years... just as more accurate info is given on basement insulation and vapor barriers. I was looking at the mold on the roof sheathing, low down and close to the cellulose at the sloped ceiling area, hope it is not coming from there (no baffles pictured). If after bath fan venting; shows new mold, the OP knows where we


Hi Gary,

It may very well be that a lot of that gray we are seeing came from that blown in cellulose when it was blown in against the underside of the plywood. I would personally never use that crap again as an insulation. It likes water.
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