Foundation Sill Flashing Under Siding


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Old 01-19-22, 08:18 AM
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Foundation Sill Flashing Under Siding

I have a 1930's cape style house in southern New England. The whole house has cedar shake siding. The exterior walls of the original house all have sill flashing at the base of the foundation (some of these walls abut the sill, others sit back 1/2" or so). A new addition, which is on slab, (done by previous owners) does not have any observable flashing along the base. In some areas, the last row of shingles overlaps the slab but in most, it ends right at the top of the slab without any overlap. I even found some areas where it lands on the top of the slab.

The "new addition" has horrible cold air infiltration along the baseboards inside. I suspect its coming at the sill. While walking the exterior, I noticed an area where I could gently pull forward the bottom row of shingles and actual see the sill plate. After seeing where some shingles end and the lack of flashing, I suspect there may also be water infiltration now too.

Some questions:

1) I think it's not good that I can see the sill plate. Can I shimmy some flashing up the back side of the last row or two of shingles to protect it from water infiltration??

2) I also believe the cold air infiltration is occurring along this sill. Any ways I can insulate from the outside? The few areas with large enough gaps, I used spray foam. I am wondering if there it insulating sheathing I can place along the back side of the flashing before shimmying it up behind the shingles?

Thanks



 
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Old 01-19-22, 08:31 AM
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1. You should not see the sill plate. Whether or not you can get flashing installed depends totally on your house. You might be able to slide flashing up part way but you shouldn't be able to get it as far as you want. You will probably have to remove shingles to get flashing up as high as it needs to go.

2. You won't be able to do meaningful draft stopping with the shingles in place as it needs to be installed underneath the shingles. You can try caulking/foaming what you can see but you shouldn't have luck sliding anything under the shingles.
 
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Old 01-19-22, 09:39 AM
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Thanks for the quick response, PD.

With regards to cold air draft, I am probably better off removing the baseboard on the inside, cutting back a couple of inches of sheet rock behind it and spray foaming down there.

As for the flashing, how high should it typically go behind the shingles? I would think at least to the overlap of the second line of shingles, which is about where nails will be that fasten the bottom row???

Thanks again.
 
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Old 01-19-22, 09:55 AM
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There has to be wall sheeting under those shingles with some type of membrane / felt paper you will not get access to any of that from the inside.
 
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Old 01-19-22, 09:57 AM
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That is a section over a door/window but it shows the components.


 
  #6  
Old 01-19-22, 10:56 AM
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Thanks. Very helpful image. I can tell there is the black paper like moisture barrier between the plywood and shingles.

Ill try to find time to investigate more Saturday morning.
 
 

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