sill plate overhang on slab foundation

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Old 03-19-13, 07:34 AM
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sill plate overhang on slab foundation

I am replacing siding on my house which has been damaged from moisture. I am finding the slab was surrounded by apprx. 2 inches of styrofoam which was then covered around the outside with a 1x4 board and the siding extended over the board. No wonder the damage. Since the rotting boards and styrofoam have to be removed I am finding the sill plate now extends 3 to 4 inches from the slab. The walls are 2x6 studs. Is this safe, the sill plate is now exposed? How can this be repaired?
 
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Old 03-19-13, 12:43 PM
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If the sills are rotted, they need to be replaced. If just exposed and cantilevered, but in good condition, they should be given a heavy dose of preservative treatment (something with copper napthanate in it, the dark green stuff), allowed to thoroughly dry, and then covered with Z-flashing before installing new siding. If already treated with preservative, indicated by incising in the wood surface, the sills wouldn't need any copper napthanate.
 
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Old 03-19-13, 01:13 PM
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Hi jk,
Exterior foam insulation on slabs and foundations is a common practice to reduce heat loss. The foam then needs to be covered for physical protection and to prevent attack from insects. The approach to the latter varies by location. I was too young to think about things like frost depth when we lived in Salina, but my guess would not real deep. If you choose to replace the foam, at least 1" thick, I would recommend going down at least the depth of the slab and then sloping out 2'. Some foam is available pre-treated for insects, but also treat the soil. there are several environmentally friendly treatments.

For the exterior covering, here is a GBA article:
How to Finish Exterior Foundation Insulation | GreenBuildingAdvisor.com

And as BridgeMan suggested, be sure your sill plate is PT or properly treated. If the soil is too high, less than 6", I would recommend some landscaping with proper drainage to keep the water away from the siding.

Bud
 
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Old 03-20-13, 08:36 AM
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So far I have found only minor damage to the sill. Your suggestion on preservative treatment is great but leads to another question. Is the house structurally sound with the cantilevered sill?
 
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