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captainrichhill 05-03-2010 08:19 PM

Hi everyone,

I am installing Hardiplank siding on my home in Jacksonville, FL. I was thinking about adding the R-MAX 1/2'' ridgid foam with the foil backing on both sides for additional R value.

My questions are these:

1. Do I still need to wrap the house with tyvec or can the R-MAX be my vapor barrier if I tape the seams in the foam?

2. With the added thickness of the insulation board will that cause any problems securing the Hardiplank to the home? What size nails?

Any suggestions or tips would be greatly appreciated.

the carpenter 05-03-2010 09:35 PM

No you do not need any tyvek.
To correct your lingo, tyvek is a weather barrier NOT a vapor barrier. It is breatheable to let moisture out of the walls in case it gets in.
I am in the residential construction industry and we use the foil face and backed insulation all the time and tape the joints instead of tyvek. I'm not completely sold on the application on the house exterior. The stuff does not breathe as far as I know so isn't it like creating a double vapour barrier?
Anyways, that's my disclaimer. I think it's a great product. We put hardie over it all the time. We did have an issue in a windy area where the wind actually worked a couple of pieces of siding right off of the wall but I think that the boys had their nails set too deep. Hardie doesn't want you to countersink the heads at all and I think that the rigid insulation just gave enough play along the top edge to work the nails through the board. The nails didn't pull out, the board just worked right off of the nail heads. We've never had it happen on any other jobs. Hardie probably has a recommended fastener penetration into the studs. Talk to your local inspector for his two cents on the foil insulation. Good luck.

captainrichhill 05-05-2010 08:34 PM

I spoke to a building inspector tghe other day and he said that a house wrap wouldn't be necessary. He said that the house is already wrapped and you don't want a double vapor barrier. Isn't that what I'll be doing if I tape all the seams? Since I've done some repairs on the old T1-11 the old house wrap hasn't retained its integrity. Some areas were torn. I guess I'll try the 1/2'' R-matt and see how it goes.

kindrox 05-06-2010 09:10 AM


2. With the added thickness of the insulation board will that cause any problems securing the Hardiplank to the home? What size nails?
My readings suggested it was best to have foam under hardieboard as it gives a little wiggle room for the concrete as the house shifts with the seasons. I used .75 inch foam RMAX.

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