Ask the Builder: Replacing a foundation can be done, but find the right contractor

Q. I’m thinking of buying a house that has a crawlspace. The foundation is in very bad shape. While the house looks quite bad, it’s got good bones. Is it possible to completely remove a bad foundation and install a new, taller one? What’s involved? Who does this type of work? What would you make sure gets done if you’re going to all this work? – Hanna S., Hartford, Connecticut

A. Anybody buying such a dilapidated house needs to negotiate a really good deal. The good news is that the old foundation can be removed and replaced with a new cast-concrete foundation, creating a full basement. The task is not much different from eating an elephant. You just take one bite at a time.

Hanna’s question reminded me of a fascinating time early in my building career. Fresh out of college, I had just rehabbed my first house in Cincinnati. It didn’t need a new foundation, but it was otherwise in pretty bad shape. Four months of work transformed the house back to its former glory.

About a half-mile away, a developer wanted to put in a small shopping mall, but there were about 10 houses and an apartment building in the way. Not only did he buy all these properties, but he proceeded to move them about a mile away on some wooded land he bought at the end of a street. I remember watching these houses, and parts of houses that were cut in half, creeping down the road to their new foundations.

Hanna needs to contact different foundation contractors to see which ones have done exactly what she wants to do. Not all foundation contractors have the expertise to work underneath a house that’s suspended above the work site, sitting on cribbing made with timbers the size of railroad ties.

These foundation contractors also will know the names of the different house-moving companies in the area. The first step in the process of tearing out the old foundation and installing the new one is to prepare the house as if it’s going to be moved to a new location. House-moving companies do this like you might brush your teeth. It’s just another job for them.

I’d consider several things if this were my job. For starters, I’d want to make sure the house was lifted high enough so there was positive drainage away from all sides of the house. The building code’s minimum standard is 6 inches of fall in the ground in the first 10 feet of horizontal distance away from the foundation. I feel 12 inches of fall is much better.

If the budget allows, I’d also try to pour the new foundation walls as high as possible so a true 8-foot ceiling height might be achieved in the basement. Hanna needs to make sure a great high-performance vapor barrier is installed under the new basement concrete floor.

I also would install interconnected, perforated 4-inch pipes beneath the new basement slab to capture radon gas that might be seeping up from the local bedrock. A riser pipe that connects to the below-slab pipes should then be extended up to the roof to vent the radon.

Q. I’m about to install ceramic tile on a concrete floor of a 40-year-old house. The concrete floor has cracks in it. This is a DIY endeavor, and I don’t have the extra money to install the expensive membrane that I should use. Are my new tiles going to crack? What would you do? What about grouting the tile? – Sarah H., League City, Texas

A. Sarah’s got spunk. I applaud her spirit, and she can achieve success if she does a few simple things. There are different crack-isolation membranes that uncouple the tile from the actual concrete slab. She might price all of them to see if there is one she can afford.

There’s not a doubt in my mind that the new tile will develop cracks directly on top of the cracked slab if no membrane is used. Since Sarah’s budget is tighter than a banjo string, she might take a chance using two layers of 30-pound felt paper. This is a very affordable material, and while I’ve never used it as a tile crack-isolation membrane, I feel it’s got a fantastic chance of performing quite well.

If the cracks in the slab are wider than 3/16 inch, I’d first try to bond the concrete together by injecting a high-strength epoxy into the crack. This will go a long way to prevent future cracked tile.

I’d then install the felt paper just as you would one of the fancy membranes. This requires a bed of thinset adhesive that you then cover with the first layer of felt paper. Smooth the felt paper using a rented linoleum roller. Be sure to install the felt paper so it crosses the cracks at a 90-degree angle if possible.

I’d then install the second layer of felt paper over the first layer at a 90-degree angle. I’d not install any thinset between these two layers. The weight of the thinset under the tile and the tile itself will press this layer against the first layer.

Once the tile is installed, Sarah should go to my website, AsktheBuilder.com, and watch my four-part video series about how to grout ceramic floor tile. She’ll get professional results with a minimum of practice.

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