# ridgid insulation under new siding



## PeterQBrown (Dec 13, 2010)

This topic has no doubt been discussed, but I am new to contractor talk and cant find it.
I am about to re-side an older home here in Bozeman MT. Wall construction= Asbestos cement shingles (now removed) over 30 lb felt, over 1x6 sheathing on 2x4 walls with fiberglass insulation and plaster board wall covering. This home does NOT have a plastic vapor barrior on the warm side of the wall. 
I will be using CertianTeed fiber cement lap siding. I want to add a layer of 1/2" rigid Insulation to minimize thermal bridging and cut down air infiltration. My current insulation choices are 1/2 "closed cell blue (non faced) ridgid insulation or 1/2" foil faced rigid insulation. I dont want to create any condensation problems. foil faced insulation creates a impervious vapor barrior for sure. Anyone want to weigh in on this?
thanks for your time
pb


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## woodworkbykirk (Sep 17, 2008)

1/2" foam doesnt offer a whole lot for r-value, we use 1" on every house we do the siding on, depending on supplier cost we bounce back and forth between extruded 1" (blue or pink) or enerfoam which is foil backed and faced. i should mention a good portion of the homes we do are reno and fit the same description as yours to a T. we generally use harti so we put on 1x4 for rain screen in the warmer months but switch to 5/4 in the winter just so it doesnt split all to hell when we shoot it on when its frozen.

there are some foams which are perforated but need tyvek over them. if the house is a complete reno, you should talk to the h.o about putting in a venmar it will definitely help with keep the relative humidity down


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## SLSTech (Sep 13, 2008)

Good points by Kirk and I agree on the 1" at minimum (2" might be nicer & eliminate your worries about perm ratings, etc...) - as an FYI Venmar equals a brand name ERV / HRV in his neck of the woods

You might also want to check out BuildingScience.com for some wall assembly details that detail best practices in your climate


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## PeterQBrown (Dec 13, 2010)

Minimum 1" sounds reasonable
1. Are you using the fir strips for a ventilated space or for nailing surface for the siding?
2. Do you have any problems with wavy looking walls?


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## SLSTech (Sep 13, 2008)

Installed properly, you wont as you can fir out the strapping to keep it nice & perfect if there are issues with original building

You could also consider using a cedar breather product to aid in draining / ventilation while either adding insulation &/or keeping depth down

For example 1" foam followed by 1x strapping with foam in between strapping followed with breather


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## woodworkbykirk (Sep 17, 2008)

i should mention the flashing details with this type of rain screen is more diffuicult, we go through vycor by the case doing homes this way. with the wood rain screen we can set our windows into caulking, if the window goes directly onto the foam you cant back caulk as it will eat the foam


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## Tom Struble (Mar 2, 2007)

you could fur out the windows with wood


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## PeterQBrown (Dec 13, 2010)

not sure I really understand here. My understanding so far is adding foam of any thickness to the exterior and taping joints against air infiltration essentially seals the walls from passing accumulated cavity moisture to the outside (drying the cavity). Firing strips are a nailing substrate only. leaving the air gap between the fir strips allows air flow and drying should liquid water get past the siding. But I could fill these gaps with foam as well.

My original intention with the 1/2" foam was to impede thermal bridging. I feel confident that we could easily nail through siding and 1/2" foam. I Just looked at this home again this afternoon and going 1" plus furring strips adds a whole host of thickness issues that are deal breakers. It would be wonderfull to add 2" of foam, but realistically thats not feasible without major cost and esthetic problems. It looks like it is 1/2" or nothing. It seems a shame to just re-side with no insulation added, not even 1/2".


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## Tom Struble (Mar 2, 2007)

you can do what you propose,it's in hardies thermal performance technical bulletin


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## lshomesolutions (Jul 19, 2008)

I would pull off the 1x6 sheathing. Make sure insulation in the 2x4 cavity is good. 1/2 sheathing ( foil backed), house wrap it , and hardi.


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## Tom Struble (Mar 2, 2007)

really? just pull the sheathing?you have no concerns with possible racking?


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## SLSTech (Sep 13, 2008)

lshomesolutions said:


> I would pull off the 1x6 sheathing. Make sure insulation in the 2x4 cavity is good. 1/2 sheathing ( foil backed), house wrap it , and hardi.


 :no:

First, you need to leave the sheathing & you can also skip the foil backed foam because if you don't have a 1" air gap it isn't going to reflect any radiant heat.

House wrap should be put on the sheathing with cap nailers & taped - then the foam & the seams taped on that. 

Then you should either utilize a cedar breather product or furring strips to not only help straighten the wall out but allow any water that gets past the hardi to drain out. That is the best practice - can you get away with out furring strips or cedar product sure, but then you can get water trapped between the foam & hardi product & any gaps not sealed will allow water in


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## PeterQBrown (Dec 13, 2010)

Thanks guys, this is all great info. I appreciate your time.


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## Tom Struble (Mar 2, 2007)

house that old probably has a few layers of oil based paint pretty much providing an interior vb


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## PeterQBrown (Dec 13, 2010)

vb? what is that short for?


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## CookeCarpentry (Feb 26, 2009)

PeterQBrown said:


> vb? what is that short for?


Vapor Barrier.


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## Tom Struble (Mar 2, 2007)

check out this faom drainage system,it's only 1/4'' thick but you can install it over foam or sheathing
http://greenguard.pactiv.com/reside....raindrop#dc14-drainage-mat.dc14-drainage-mat


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## Warren (Feb 19, 2005)

Ridgid is making insulation now? 

Is it as crappy as their tools?:whistling


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## Theophilus20 (May 19, 2010)

Warren said:


> Ridgid is making insulation now?
> 
> Is it as crappy as their tools?:whistling


^^^ Thats Funny :lol:


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