Mold free attic
Last Post 30 Dec 2017 04:36 PM by greentree. 9 Replies.
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predgwUser is Offline
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05 Jan 2017 01:47 PM
Looking to build a new home (two story colonial with full basement) and because of health issues with my wife (CIRS) I need to eliminate the possibility of Mold. I'm leaning heavily on either block or vertical ICF from basement up to top of second floor. What to do with the roof is up for debate. The safest bet is insul-deck for the 2nd floor ceiling, and then wood trusses above that. The insul-deck would essentially cut off the unconditioned attic from the house. I would use a rubber boot product to seal off pipes (venting) and would not have attic access from second floor. Instead I would install a small sealed door on one gable end. This is however an expensive option. I'm open for suggestions. I have also looked at: Insul-deck poured as a pitched roof. Nudura Ceiling Technology. I would use cement board instead of drywall in attic. Metal SIP. Not sure how I would handle lighting. Metal roof joist but I still end up with wood in the unconditioned space. Typical wood roof, but with Plywood sheathing with melamine on the attic side. This would provide a very smooth surface that would be very easy to clean if mold did get in attic. This would be combine with painted trusses (same concept) and powered gable fans and soffit vents. ( don't get me stated about ridge vents in the winter). Any thoughts
Dana1User is Offline
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06 Jan 2017 11:02 AM
That's a pretty expensive option that may not be necessary. The relative mold hazard and how to manage it is climate-specific- where are you?
GaryOUser is Offline
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06 Jan 2017 04:51 PM
I had an interesting experience as an exterminator in dealing with Sick Building Syndrome and the insurance company for the building in question. One of the jobs with this insurance company was for a Residence Inn where they had mold inside the bathroom walls in a few units. Those units were stacked, one on top of the other.

This job was interesting to me because it was outside of the normal pest control world. The insurance company had powerful microscopes and laboratories to help them determine the problem. I was just hired to apply the chemicals of their choosing as requested. The chemical I was told to use was normally a termiticide, (BoraCare by Nisus) I drilled holes through the mortared tile joints about every 8". I inserted a brass spray tip that sprayed sideways in a + pattern.

While BoraCare is normally used as a termiticide, it is also a fungicide and herbicide. It can be applied to structural lumber prior to construction (or after if accessible). It soaks into the wood through capillary action and becomes a permanent part of the wood itself.

I mention these things because it may be an alternative path to preventing molds in your new structure. It's not cheap (like $75/gallon that is mixed 1:1 with water).

I suggest that you call their technical service and ask questions.
GaryOUser is Offline
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06 Jan 2017 04:55 PM
I just searched for Boracare Nisus and see they have a product for mold. It's Bora-Care with Mold-Care. $104/gallon but 5:1 water to product. Read their suggestions for dealing with different problems related to mold.
predgwUser is Offline
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06 Jan 2017 05:15 PM
I'm in northern VT. So zone 6. Most of the roofers around here use ridge vents with soffit vents. I have witnessed winters where my ridge is covered with 8" of snow minimum for a good month straight. Vent probably does not work so well then. I think a product that is less porous, combined with a paint to help seal up the wood could be a good option. A better option is no wood. I have come to realize that I can really minimize problems by 1: Proper venting and moisture control of living space. Oven vent to outside, dehumidifiers as needed. 2. Proper attic insulation 3. Proper attic sealing with correct vapor barrier. I think the Nudura Ceiling Technology may be a good option. I would use cement board against the roof trusses, then do a great job sealing things up. I believe this gives me a R49 ceiling. I would then paint the roof sheathing (underside) and use a powered gable vent. No ridge vent.
jonrUser is Offline
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06 Jan 2017 07:10 PM
Vent probably does not work so well then


Somewhere (edit: https://www.youtube.com/watch?v=Ld8pzIu45F8) I saw a report that snow is air permeable enough that it continues to work. But would be interesting to see data.

If you going to use gable fans, I'd a) make it automatic based on humidity and b) use a push-pull pair so that it never pressurizes or depressurizes the attic.

Also measure and control building pressure - this is what determines air flow through walls and ceilings. Positive pressure when the AC is on is known to reduce mold problems.
predgwUser is Offline
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07 Jan 2017 09:56 AM
Jonr

Interesting. I will look into that. Yeah, I would like to see the data on snow letting a roof vent, either way, I'm not taking a chance.

Looking at the Zip roof sheathing, the product has a radiant barrier on the the underside. I suspect that will help protect the OSB from any possible mold growth as well. Again, a surface that is smooth and easy to clean.
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01 Feb 2017 11:12 PM
( I have come to realize that I can really minimize problems by 1: Proper venting and moisture control of living space.)

The answer is in isolating the attic space from the house entirely.
If you do this, the mould in the attic would not bother the residence. But more importantly, moisture will not infiltrate the attic from the house so you won't have mould in the first place.

I know some forum regulars don't appreciate the finer aspects of poly but that is the way to go in this case. I totally understand that it stops inward drying but we are talking about a vented attic. Additionally with even R30, the poly will be at the same temperature as the drywall ceiling so will not be anywhere near dew point. Just like putting insulation of the roof deck to protect it from condensate.

Located in Northern Vermont you would be in similar climatic conditions to southern Quebec and are further north than much of Southern Ontario. All of Canada has used poly air barrier for more then four decades with no ill effect. The space above is vented so any moist the insulation takes on will be from outside and will dry to the outside again.

Detailing is everything but not that hard. If you install internal walls, insert a 18" width of 6 mil poly between the double top plates. If you have light outlets in the ceiling, use vapour hats http://www.rona.ca/en/vapour-barrier-0320352--1
Any holes drilled through the top plate poly (by electricians etc.) must be sealed. Use acoustic caulk. It never harden and never shrinks. Just stick the nozzle in and give the gun a couple of cranks. If there is more than one wire running up, take the time to squeeze a little between each wire. When the wiring is done, install 6 mil poly over the whole ceiling. Seal all seams with acoustic caulk and let the poly drape down the ICF wall a foot or two. Carefully cut the poly around the light outlets and insert the tip of the caulking gun between the vapour hat and the poly to create an air tight seal.

The only other item that should penetrate the vapour barrier would be you plumbing stack. Use a neoprene flashing similar to the roof flashing and seal the vapour barrier to it.

Bathroom and kitchen fans should not vent through the attic if at all possible. As a rule, I locate bathroom fans high up on the wall and vent DOWN the wall and out the joist space. Fans vented UP always allow cold air to drop down.
Better yet, use an HRV. Better control.

If at all possible, locate your attic access outside through the gable. Attic accesses rupturing the ceiling air barrier almost always leak some air. Additionally, when you have to use them, you usually drop debris into the house.
If you do all this with proper care and attention, you will have an air tight separation between the conditioned space and the attic. You will have no infiltration induced mould in the attic.

AND NO, HVAC does NOT belong in the attic!
patonbikeUser is Offline
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02 Feb 2017 01:17 PM
I am in VT with a a colonial. The 2nd story ceiling is sealed from the attic. To simplify this we do not use any recessed lights on the 2nd floor. Whatever electrical boxes, fans, pipes, etc. are caulked or foamed after installation. I think it is continuous ridge and soffit and don't have any reason to think mold is an issue. There is no mechanical ventilation in the attic.
It is a metal roof and the snow does not like to sit up there for very long at all.

The access to the attic is a very tightly fitting thick piece of rigid foam (don't actually know the R value) that is spray foamed along the edges. So it's basically semi-permanently installed.
greentreeUser is Offline
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30 Dec 2017 04:36 PM
I think building a new house working under the assumption mold IS going to form in your attic and spending a lot of money to isolate the possibility is the wrong place to put your money plus counterintuitive.

Ive done a lot of remodeling, restoration and home performance retrofits in zone 6 and 7 so Ive seen a lot of mold in residential and commercial spaces in basements, walls, attics, under assemblies with exterior and interior sources of moisture and Ive seen even more mold free spaces. Ive worked on some spaces that needed professional remediation, usually improperly winterized foreclosures.

The only time I can think of we have come across attic mold it was either a roof leak, condensation issue driven by lack of insulation or an exhaust vent terminating into the attic (most common cause/condition), or a framed dropped soffit over tub or shower that isnt blocked at the ceiling plane helped along by insuffcient or under utilized bath exhaust (hundreds of attics).

Blanket observations: Most of the time mold presence is because of exterior flashing details, starting at window or door upper corners and fanning straight down in a big triangle or the infamous missing kick-out flashing. A lot of times you can poke your finger right into the wall.

Almost always come across a patch of mold in bath remods even when the bath is in pristine condition. It will be under the flooring along the tub or shower module, under the flooring under the toilet, and usually always behind the toilet tank. Usually insde the tank as well.

Most of the time these discoveries are made while in process of doing something else, dealing with the defect that caused the mold wasnt in the scope of work since there was no indication that should be an issue, but when the finish material (siding/stone/stucco/EIFS/flooring/drywall/insulation, ect) was removed the moisture source became obvious.

So put your money in the fundamentals unless you have deep pockets because good fundamentals require a really good contractor and that alone will cost more plus the extra material cost will add up quickly. Exterior flashings, interior details in moisture source areas, whole house and point source humidity control, interior air filtration, natural materials, no carpet, maybe design the house to be durable in a positive pressure environment. The more airtight you make the house, the more careful you should be.

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