Latest Discussions : HVAC


03:00PM | 04/07/04
Member Since: 04/06/04
2 lifetime posts
I'm restoring a 100 year old house in the Bay Area (CA) and want to insulate the exterior walls without removing the skip sheathing and siding and there's no existing moisture barrier. I'm concerned about trapping moisture in the wall cavity. Several things have been recommended, including adding tyvek on the inside face of the studs (they're all exposed to the interior); plastic-wrapped batt insulation and "cedar breather" to keep the air flowing. Can I omit the tyvek (as it seems to invite condensation)? Will the insulation simply act as a condensation line, forever exposing the studs to moisture?

Am I asking for trouble here?


04:24PM | 04/10/04
Member Since: 01/28/03
693 lifetime posts
The only thing that should be required for your situation is to install fiberglass batts with kraft paper facing or 'plastic' wrapped fiberglass batts and nothing else.

The only exception is that you would need to make sure that any wrapped plastic batts you use is truly a 'vapor barrier' since not all wrapped fiberglass batts act as vapor diffusion barriers.

But here is the long and short of your situtaion in a nutshell:

For a climate such as yours, any vapor barrier should be placed on the inside, under thed drywall. This is most easiest achieved by using kraft faced or wrapped fiberglass batts with the vapor barrier alingned to the living space of the house.

The reason you want to do this is because the interior air of your will most often be the warmer and therefore the moister air.

By controling the flow of this moister warmer air into colder stud spaces, you can eliminate or reduce condesnation problems.

Not only does the kraft facing or the wrap on fiberglass batts act as this vapor diffusion barrier, so does the interior paint on your walls, the drywall or plaster itself, any paneling and so forth that covers the interior walls.

So for all intents, the ONLY thing you need is kraft faced or wrapped fiberglass installed in the studs and nothing more.

No Tyvek.

No Cedar Breather.



08:00AM | 04/12/04
Member Since: 04/06/04
2 lifetime posts
Thanks, Handyman!

I've had tons of advice from many directions about this and although there's no clear consensus there are some common themes:

No Tyvek. it will just promote condensation on the back of the gyp board.

Wrapped Insulation. keeps it from acting like a sponge.

Low permeability paint in moist areas.

However, the cedar breather acts like insurance for all parties involved. A feel good measure for a couple grand.

anyway, thanx again.


07:28PM | 08/15/05
Member Since: 08/14/05
18 lifetime posts
I am replacing my old, damp asphalt siding on my 100 year old twin in NJ. Every contractor has said something different about what type of inuslation to put up under the new siding. One says extruded polystyrene with no moisture barrier to allow the walls to breath. One says tyvek. One says styrofoam insulation with a moisture barrier under the siding. What do I do???

Keep in mind, I have a damp, moldy basement, the moldy air has access to the channels in the exterior walls, no insulation at all to speak of, crumbling plaster in some spots, drywall in others. HELP!


03:11AM | 08/16/05
Member Since: 01/28/03
693 lifetime posts
First things first.

Deal first with the basement moisture problems and it won't much matter how you insulate your walls.


04:39AM | 08/16/05
Member Since: 08/14/05
18 lifetime posts
Wow. Thanks for the quick response!

As for the basement, I am proud to say that I am working on it myself. I am installing ventalation fans, gutting everything I can to get down to the cinderblock walls, bleaching it all, patching any and all cracks, and coating it with a waterproofing paint. Unfortunately, there is nothing I can do to cure the problem. Since it is a twin, the walls under the additions are up against the neighbors lawn. If I could go install a concrete patio for them, things would be great...but I can't.

So, given that I will always have at least a small moisture problem...what should I do under the siding? Any other recommendations for the basement?

Thanks for all your help!


10:34AM | 08/16/05
Member Since: 01/28/03
693 lifetime posts
If you have a baloon framed home, you should install fireblocking at the basement sill plate to prevent air flow up into the wall cavities.

Sealing the fireblocking would also help control air flow and basement moisture up into the walls.

Insulation should be kraft faced with the vapor reatrder on the warm in winter side of the insulation. This is the area directly under the drywall and over the studs.

If you choose to install rigid foam on the outside of the sheathing directly under the siding, you will install foam only with no weatherbarrier such as Tyvek.

Tyvek is not a vapor retarder. It is an air barrier and does nothing to prevent the flow of gaseous water through walls.

A weatherbarrier/housewrap is never used with rigid foam. It is either rigid foam or housewrap and never both.

There is no need to let wall cavities 'breathe' with rigid foam exterior insulation because the rigid foam keeps the wall cavities warm and above the dew point for gaseous water to condense.

As long as gaseous water does not condense, it will cause no harm. Only liquid water promotes rot and mold growth.

Interior vapor retarder on warm-in-winter side. Tyvek of other housewraps/weatherbarrier ok as long as not used with rigid foam. Rigid foam ok as long as not with housewrap/Tyvek.


12:00PM | 08/22/05
Member Since: 08/14/05
18 lifetime posts
Again, thank you for the info!

However, what is a baloon framed house? What is fireblocking? Will it come with directions on how to seal it?

Some of the channels in the basement are blocked off with fiberglass insulation (it is just stuffed in the square-shaped cavities where the wood frame starts above the cinderblock walls. Is this ok or should I remove it before installing the fireblocking?

Also, I understand I should not use tyvek. But, am I to understand that I should use rigid foam with or without a mositure barrier directly under the siding?




07:10AM | 12/18/19
So we have some mold in existing exterior walls of a couple bedrooms and I am wanting to fix that by adding in insulation DIY to help minimize costs.

I seen that the best would be getting sprayed in foam to help with moisture.

My question is what is my best option? I live in PNW and moisture is always high here, last year we already spent time/money doing the KILNS painting to try and get rid of mold off the walls but it has came back again.

Do I need to scrap that sheet rock (take off walls, all in insulation and then re-sheet rock) or just get something blown in holes at the top of my walls and repaint again?


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