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Old 01-26-2009, 09:33 PM   #1
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Rigid foam sheathing on top of foam insulation?


Can you think of any reason why I wouldn't want to use rigid foam insulation in my exterior wall cavities if I'm replacing my wood lap siding with rigid foam sheathing?

On a different note, has anyone had any experience with Hardiplank over foam sheathing?

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Old 01-26-2009, 09:53 PM   #2
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Rigid foam sheathing on top of foam insulation?


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Can you think of any reason why I wouldn't want to use rigid foam insulation in my exterior wall cavities if I'm replacing my wood lap siding with rigid foam sheathing?

On a different note, has anyone had any experience with Hardiplank over foam sheathing?
Is that nat gas or LP. Wrong forum this is HVAC

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Old 01-26-2009, 11:35 PM   #3
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Rigid foam sheathing on top of foam insulation?


I really dont understand your question .Your going to remove the existing lap siding?Is there sheathing under that?you want to put ridged foam inbetween the studs?You can put hardie over foam but a better way would be to install the foam then a house wrap then vertical furring strips then your siding
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Old 01-27-2009, 07:08 AM   #4
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Rigid foam sheathing on top of foam insulation?


Yes, vertical strapping for a rainscreen. All the siding manufacturers highly recommend it. I would especially think it was important over a semi-impermeable surface like foam.

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Old 01-27-2009, 09:06 AM   #5
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Rigid foam sheathing on top of foam insulation?


I may be wrong here but I thought you could not put foam inside the structure. It had to be on the exterior of the structure due to fumes in case of fire. Check with codes or better builders in the area.
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Old 01-28-2009, 08:50 AM   #6
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Rigid foam sheathing on top of foam insulation?


as long as the foam is protected by drywall its ok im just not sure why the op want to put foam panels in between the stud bays
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Old 02-03-2009, 10:01 AM   #7
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Rigid foam sheathing on top of foam insulation?


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as long as the foam is protected by drywall its ok im just not sure why the op want to put foam panels in between the stud bays
You're not sure why I would want the foam in the stud bays as opposed to fiberglass batts in the bays?
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Old 02-03-2009, 10:03 AM   #8
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Rigid foam sheathing on top of foam insulation?


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Originally Posted by strublesiding@optonline.n View Post
I really dont understand your question .Your going to remove the existing lap siding?Is there sheathing under that?you want to put ridged foam inbetween the studs?You can put hardie over foam but a better way would be to install the foam then a house wrap then vertical furring strips then your siding
No sheathing is present under the lap siding at this point. I was thinking rigid foam sheathing and rigid foam insulation in the stud bays. I think I'll take your advice on the furring strips.
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Old 02-03-2009, 10:11 AM   #9
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Rigid foam sheathing on top of foam insulation?


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Is that nat gas or LP. Wrong forum this is HVAC
LP of course. I figured the folks who are experienced at heat load calculations might have some input on how to best maintain the house envelope.
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Old 02-03-2009, 10:20 AM   #10
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Rigid foam sheathing on top of foam insulation?


oh i think i understand your going to remove the existing siding and that is also the sheathing.you have to be careful when you remove the siding your reducing racking resistance depending on how your house is built you would want to replace it with a structural panel imo.why dont you consider blowing cellulose or fiberglass into your walls leave the lap siding and installing a foam sheathing on top of the siding then tyvek then your furring and finally your siding this would be a more typical installation .There are foam wraps that are perforated to help the wall ''breathe better''usually these are the fanfold types usually 1/2 thick

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Old 02-03-2009, 03:12 PM   #11
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Rigid foam sheathing on top of foam insulation?


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LP of course. I figured the folks who are experienced at heat load calculations might have some input on how to best maintain the house envelope.
As I see you are correct. I have been following the thread and have learned a few things. Glad you posted here.
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Old 02-03-2009, 08:39 PM   #12
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Rigid foam sheathing on top of foam insulation?


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Originally Posted by strublesiding@optonline.n View Post
oh i think i understand your going to remove the existing siding and that is also the sheathing.you have to be careful when you remove the siding your reducing racking resistance depending on how your house is built you would want to replace it with a structural panel imo.why dont you consider blowing cellulose or fiberglass into your walls leave the lap siding and installing a foam sheathing on top of the siding then tyvek then your furring and finally your siding this would be a more typical installation .There are foam wraps that are perforated to help the wall ''breathe better''usually these are the fanfold types usually 1/2 thick
I'll definitely consider that route. If I leave the siding in place, wouldn't I be likely to see some unevenness in the Hardiplank?
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Old 02-04-2009, 12:41 AM   #13
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Rigid foam sheathing on top of foam insulation?


thats another advantage to useing vertical strapping you can shim it to help keep your siding looking straighter


Last edited by Tom Struble; 02-04-2009 at 12:43 AM.
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