Gothic Arch Greenhouse

Step 4 : Frost Protected Foundation

moisture protection added to our block wallAfter the block wall was completed, we still had a couple more tasks to do before we could back fill the soil.  We chose a style of construction referred to as a shallow frost protected foundation, so it was necessary to take precautions to prevent frost penetrating under the concrete. 

Because we expect  a large amount of water and snow to slide down the side walls, we first covered the exterior with ice and water shield.  Although more commonly used on rooftops, it was used here to protect the blocks from excess moisture penetration.  It took less than two rolls of ice and water shield to cover the surface so it was an inexpensive method of waterproofing the blocks.  We then used construction adhesive to fasten 2 inch foam insulation over the ice and water shield.

After the insulation was fastened to the outside, we laid additional insulation along the ground before replacing the soil.  This insulation is important to protect us from any possible frost damage.  With this added protection, it is no longer possible for the ground to freeze all the way around the insulation and penetrate under our concrete floor. 

With the foam in place, we were then able to back fill the soil and add our sill plate to the top of the wall.  We laid out 14 inch flashing over the blocks for a termite and pest barrier, and then a rolled foam product to seal under the boards.  We carefully fastened our boards to the top of the wall using 1/4" x 2 1/4" Tapcon concrete anchors.  These masonry anchors are building approved screws that cut their own thread into the block.  We used the top blocks as a guide to be sure we pre-drilled the holes into the web of the concrete block.   With the anchors inserted, the sill boards tightened down smugly to the block wall with the flashing and foam seal in between.

view of wall showing frost protection

The photo below shows our completed wall.  The grade of our yard is sloped so the top of the wall will be visible in the front but will be almost ground level in the rear.  At a later time we will stucco over the foam panels to hide them and give us a nice finished wall under the greenhouse. 

completed wall with sill board attached

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