Foundations
John Connell founded the Yestermorrow Design/Build School in 1980 and the Yestermorrow Building Group Inc. (later to become 2morrow Studio in 1982.) He taught at Yale's school of architecture for five years after which he authored the book Homing Instinct: Using Your Lifestyle to Design & Build Your Own Home, McGraw Hill, 2000. Besides teaching he is currently designing green homes that tell "stories", design/building treehouses for handicapped children, and animating short films. 2morrow Studio puts into actual practice the design/build philosophy taught at the Yestermorrow School. A small design/build firm in Vermont, 2morrow Studio works with residential and small commercial clientele interested in integrated energy-efficient architecture using the latest green and sustainable methodologies. Besides architectural design, Connell is an experienced team builder, group facilitator and educational program designer. The Yestermorrow School teaches people how to plan, design, build or renovate their own homes. It is staffed by over 40 architects, builders and artisans from all over the United States who believe that the way to improve the built and natural environments is to re-involve people in vernacular architecture.
Questions and Answers
Q: I would like your professional advice on doing the foundation for our house during this time of year (fall/winter), we're on the east coast. I've heard that there isn't any need for concern on my part, because the foundation contractor can add some special mix into the concrete when he's doing it so that the freezing temperatures won't cause future cracking. It's going to be a block foundation. I appreciate any advice you can provide me with.
A: While it is true that concrete foundations are installed during the winter all the time, it is not true that there is no need for concern. It takes much more than just a little admixture to insure that the concrete is properly cured and durable for the long run. Also, block walls are much more susceptible to cracking than poured in-place concrete. So, that worrisome warning aside, I suggest you focus on two considerations.
1.. Where are you on the East coast? Snow belt or slush zone (north or south)? I'm wondering what your future foundation has to endure. Here in Vermont, where frost is very serious, I never specify block foundations. Oh, they're used (by others), for sure, but the risk is real and the disaster stories are legend. The ground must be flawlessly drained and the workmanship perfect. Otherwise your foundation will be reduced to an endless array of mortared cracks, just waiting for a little water or frost pressure. If you're further south, say, New Jersey, and if your site has good drainage, well, perhaps block is a reasonable way to go.
2.. Who is your foundation contractor? How long has he been in business and has he done this before - many times? Placing concrete in the winter isn't something you want your contractor to learn on your house project. Find out what other foundations they've done in the winter and go visit them. Call up a couple of other foundation contractors and ask their opinion of installing a block foundation in your area during the winter.
Don't get me wrong, it's perfectly possible to put in a top quality foundation even in areas that regularly have deep frost. But a foundation is more than just concrete. It's proper excavation, drainage (on the walls as well as around the house), insulation (even under the slab), careful backfilling with the right material and well installed concrete with proper amounts of steel reinforcing. Contractors who have done it before will stand by their work and they will tell you right up front that it's going to cost more.
I'm not trying to be needlessly scary here but, let's face it, foundations are really hard to fix after there's a house sitting on them.
Build to last! PS - at the risk of shameless self-promotion, I've included a lot more on this subject in my book, Homing Instinct, available on this page.
Q: I am building a house in myrtle beach, SC. The house has wood frame, aluminum siding and brick veneer front. My wife wants to build a 3 foot concrete walkway around the house I proposed this to the builder's superintendent and tells me that when it rains the water will stay on the concrete and rot the siding and could cause us a problem with termites and mold which is a problem in this market. Is this true???
A: I'm afraid your super is right. Placing a concrete apron around your house will likely promote rotting of the sills, siding and everything at the base of the building. Not only will rain collect and drain into your foundation, but the rain coming off the roof will spatter up against the base of the house walls. A better solution would be a pea gravel pathway around the house. This will make a nice, low maintenance pathway PLUS it will reduce spatter from the roof dripline. If you need a hard surface, then consider any of the porous, fast draining landscape surfaces that can be found on the internet. Just Google "porous pavement" and you will find plenty to choose from. But if you go this route, you must still make sure that the base fill is positively drained away from the house. I think in the end that will make it too expensive, so I suggest you consider the pea gravel.
Q: I would like to know what the difference is between a slab foundation vs. a stemwall foundation in house building? Also what are the advantages and disadvantages in them both?
A: (Kelly) A slab foundation is so-called because it creates a slab of concrete (usually between 4 and 6 inches thick) that can be used as a base for the first floor of a building. The edges of this slab are thickened and reinforced to serve as a foundation for the building as well, so that in one monolithic pour, both a foundation and and floor are created, with obvious advantages.
A stemwall foundation is usually created just around the periphery of a building and serves solely as support for the walls that are built above it, and perhaps as basement walls. This type of foundation must be dug down into the ground to get below the frost level in your area, whereas the slab can be much shallower.
Q: I am building a small home and would like to avoid pressure treated wood at all cost. I have been planning on using cedar for sill plates. Have you heard of doing this? Are there reasons why this is or is not a good idea? The concrete foundation walls will extend at least 18-24" above grade when I am finished.
A: Cedar is a little soft for sill plates but it's not a ridiculous idea. Best to see if you can get "structural grade" cedar. With your foundation walls that high out of the ground you might be perfectly safe using doug fir as long as you use a foam sill sealer between the plates and the concrete to prevent condensation. To be doubly sure, paint the sill plates with Boron solution or a good anti-fungal paint.
Q: Do you have or know where I could get a step-by-step how-to on building Stemwalls?
A: Get a copy of Homing Instinct by yours truly. I think I included an illustrated step by step of that very exercise.
Q: We are looking at building a papercrete house on a rubble trench foundation. Everything I read says the foundation needs to be below the frost line. Frost line is 36" in our area. The question is, I did some test digging where we want to build the house is and at 24" I hit solid shelf rock. Can I build my foundation on top of the shelf rock or should we consider a different type of foundation?
A: (Kelly) I suggest that you go down to the bedrock and call it quits on digging. The reason to get below frost level is to avoid the potential of upheaval from freezing soils. Well, if you are down to rock, this is not going to be heaving upwards, so you don't need to worry about it. Just go ahead with your rubble trench foundation from there.
Q: I need the formula for finding how much concrete I need for a slab. Can you help me?
A (Kelly): To find the volume of a concrete slab, you multiply the square feet of the space (length X width) by the thickness of the slab in feet (6" would be .5'). So a 30'X40' slab 6" thick would be 30X40X.5=600 cu. ft. Then you need to convert this to cu. yards by dividing it by 27, so in the case above, it would be 600/27=22.2 cu. yards.
Q: I'm building a house and have a question about how to build the front entry. The first floor joists are 2x12 which sit on the sill plates on the foundation walls. When I grade the area in front of the house, I will have the dirt at least 4-6" lower than the sill plate level to keep clear of termite or rot problems. My question is: what do I do for the entry? Is it standard practice to pour concrete steps right against the sill/floor joist bands? It seems that this would create moisture & insect problems. What are the standard practices for this/ other ways to get into the house?
A: I usually create a front step from large field stones or other dry laid masonry. This is sturdy and attractive (much better than concrete) and it allows water to drain and air to circulate. Regardless of what you decide, don't pour concrete directly against the wood. Even if you were to lay in block or stone, I would protect the wood with bituthene or similar flashing.
Q: I am preparing to build an A Frame cabin (20X20) next to a free flowing undammed medium size river. The building site is about 6-8 ft higher than the river at normal flow. I expect that there will be some periodic flooding. I want to use post/piers for the foundation, probably 6X6, and elevate the house an additional 6 ft. The soil is hard packed silt/dirt with some rocks. I was hoping to use yellow locust for the posts but I cannot find any mills locally that provide this as the locust generally doesn't grow that large in WV. My questions: Any other wood I can use? How deep should I go with the posts? What kind of spacing for the posts? Should I concrete them or not? Any other suggestions I should consider?
A: (Kelly) I would never put any kind of wood directly into the ground, if you expect the building to last more than a few decades. It is much better to place such posts on durable piers made with concrete or stone, and brace them in place so that they don't require support from the ground to keep them erect. In this case, almost any kind of wood can be used, although rot-resistant wood is best. I would try to keep the level of the posts above the level of where you can reasonable expect flooding; raise the masonry piers up that high. As for size, it is not uncommon to support houses on 4X4 posts, at about 8' intervals. Anything larger than this is good. The spacing depends as much upon the size of the beams that are being supported as the size of the posts...
Q: My home has settled and the ground around the home appears to have raised so now there is a negative slope toward the home. The bottom edge of the siding shows some moisture damage. Is it possible to cut off the bottom 8 - 12 inches of the existing siding, replace with flashing, and then add fill dirt just below the "new" bottom edge of the siding? My goal is to drain water away from the house without having to regrade my entire yard.
A: Your suggestion follows a certain logic but in practice I don't think it will solve your problem. Without seeing the exact situation, I would suggest jacking up the entire structure (8 - 12 inches?) and extending your foundation up to meet the new elevation of the house. This new section of concrete or block or brick needs to be carefully waterproofed at the joint as well as all the way up to your sills. Then, to be fully secure, you should install adequate drainage to insure that any water that might collect around the foundation is carried away. Once all of this is in place, you should be able to back fill your house and still sleep at night! Again, this is the best I can suggest without seeing the situation in detail. Good luck with it. People have had to deal with worse.
Q: I would like to add a garage stall to my house and would like to use a rubble foundation. I've spoken to a structural engineer and, although he had never heard of it, he was positive and thinks it would work. My question is do I have to tie the rubble foundation to the existing garage foundation? If so, how would I do it?
A: There's really no way to connect the rubble foundation to your existing poured-in-place foundation. Your best bet would be to compress the heck out of it before building. The new bay may well settle a bit over the first year or so. After that, it should stabilize. This is something you would need to address even if you were pouring a conventional foundation. If there's to be a slab, it will improve things a lot.
Q: I would like to build a garage on a natural rock by first putting down a cement pad. I'm concerned about the frost line because I was not thinking of cutting into the rock but rather placing my pad on top of the rock. Should I put down maybe crushed rock prior to the cement foundation for drainage or will I need drainage?
A: (Nabil Taha) Frost depth is for soils like clay, sand or fractured rock. If you have sold rock, you can build on it directly. The drainage is a different matter. If the finished grade is above the finished floor of your garage, then you need drainage. You need to check with your local building department and maybe with a local soil engineer who knows your area.
Q: I am going to build an addition onto our 1999 double wide home that is set on block skirting. I was thinking of using concrete posts with a wood post on top, exposed on the interior to hold the roof load. I was thinking around 8 or 10 foot apart for the posts.
A: (Nabil Taha) What you mentioned make sense as long as you have tie-downs, or other means, to resist the wind and seismic forces. I recommend that you check with local license engineer.
Q: My long term goal is to build a small house with a rubble trench foundation and natural rock stem wall with posts and strawbale above that for all exterior walls. I also want to use an insulated apron extending from the top of the stem wall to below grade, like in a frost protected shallow foundation, only with the apron extending out from the house nearly horizontal and the whole thing protected from rain by a wrap-around, roofed over porch. I'm a little unclear exactly where to set the posts, however. Do they protrude into the rubble foundation (below grade), rest on the top of the rubble (on grade), or with the bottom of the posts embedded in the stem wall (slightly above grade but below the top of the stem wall)?
A: (Kelly) From my own experience, I would say that the posts should definitely not be placed below grade, but could be either a bit above the rubble trench on a concrete pad or embedded in the stem wall, as long as moisture is kept away from the wood over time.
