Adding CI to old house in MD
chrislene
| Posted in General Questions on
Hi,
Old ranch has fiberboard sheathing over 2×4 walls with what seems to be faced fiberglass insulation (R13 maybe). We are not removing interior sheetrock. But we are residing the exterior and adding new windows. Can we add 1″ OC Fomular 150 against the sheathing covered by TYVEK without violating any condensation/permeability rules?
Thanks
C
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I had to google that product to see that OC stands for Owens Corning, lol.
What type of siding will you be putting over the XPS insulation? Will you be using furring strips? What will the entire assembly be?
Alside Ascend composite siding. We will attach foam to sheathing, taping seams, then Tyvek over that detailed in the typical fashion. Composite siding over the Tyvek.
Should the house wrap not be installed to the sheathing prior to the exterior insulation?
Housewrap can be installed either behind or in front of the CI. Neither is necessarily better. Either way, it is important to detail the flashings and joints to exclude water at the face of the "drainage plane," which is often the housewrap on houses that have it. Personally, I like the housewrap behind the foam primarily for the ease of sealing it to the openings and other features. YMMV
This will be the first time using ci for my builder. We are also furring out the new construction windows to be in plane with the insulation. I am thinking that wrb over the insulation is so much like flashing w/o ci that it will be easier for builder. Also thinking of taping around the furring/buck to make that extra watertight. Have also been thinking of adding a piece of under flashing at windows to kick water from integral window j channels over the siding . Have to keep details simple and basic or contractors will run for the hills. Thanks
"Old" fiberglass insulation in a 2x4 wall is probably R11, which was the standard R value for that type of insulation in that depth wall cavity for a very long time. Maryland looks to be entirely CZ4 from the IBC map I have, which would need R2.5 as a minimum based on Martin's classic article, or R5 to meet code. You'd need to go with R5 here for code reasons, which is also plenty to satisfy the rules in Martin's article about insulation ratios too. 1" Foamular (XPS) is rated R5, so you should be good to go here.
Note that polyiso is a greener option than XPS, and can often be found cheaper if you have an insulation reclaimer in your area. 1" polyiso will get you R6.
Bill