Double Sill Plate Question

[VannL]

To help even out the small ups and downs in my cinder block wall, I have been told that using a double sill plate and shimming is best. The question is about installing the top plate.

I have the bolts for the bottom plate installed in the cinder block walls. No problem and to code. Would I just install the top plate on top of the bottom plate? The seams would match.

Am I missing something or ?

Thanks.

[Redoverfarm]

This is not uncommon unless it is extremely bad.  Personally I would not see the advantage.  There is foam sills that are generally applied between the block/concrete wall and the sill plate.  Although the 2X material might seem rigid when they are drawn down the same deficit will occur just not as prominent.  You would probably be better off using a string line once you draw them tight to show just how uneven they are.  Then go back and loosen, shim and retighten.  If you do choose to double plate the seams should not fall at the same location.

[VannL]

Could I shim between the block wall and the sill plate? If I do, the good thing is that the gap under could be filled with caulk and/or more sill gasket, and it goes under the house and not into any walls.

I do plan on putting a sill gasket down, I just wanted to get everything in order first.

[NathanS]

Do you have any idea of the scale of fluctuation? In my opinion 3/8th and less I would not worry about much. If more, I would shim the sill and then pack the area between sill plate and block with a relatively dry mix of portland and sand or S mortar.

Are you worried about out of level or air infiltration?

[VannL]

It is at worst 3/8th to maybe 1/2 of an inch. My main concern is level. I want this to be as level as possible and without deflection in the floor.

Thanks.

[JRR]

I like to top off a concrete block footing wall using solid "cap" blocks.  They are available in 2" and 4" thicknesses.  Then I lay a full perimeter of strips cut out of roll roofing using (quick drying) "patch" roofing cement as adhesive.  Layers can be added to correct unevenness in the masonry.  The wood sill plates are put in place and bolted down before the roofing cement sets.   I feel the roll roofing material adds a bit of thermal and moisture separation between masonry and wood.

[VannL]

But where would you put the plate gasket?

[JRR]

I've never used a commercially available sill plate gasket.  (Kinda dating myself here)   If the cap blocks were level enough; today, I would probably use the sill gasket and forget the roofing material strips.