My wife and I are restoring/un-renovating a 1912 two story four-square. Part of the project invoves fixing a single story addition added sometime in the ’80s. Unfortunately the addition has an unheated crawl space with a questionable foundation. The original structure has a full basement with concret footings at about five feet below grade. The foundation walls are concrete block. The addition is 25 feet wide (same width as the original sturcture) and ten feet in depth. The foundation consists of five 10 inch dianeter concrete piles of unkown depth. They are placed at each corner of the addition with the fifth in the middle of the long, outside wall. The floor is constructed of fir 2×10 joists running parralel to the long wall. The joists are 12 foot 3 inch in length. Rim joists (no hangers) support the floor joists at either end of the structure. The rim joists are supported by the corner piles. There is a centre joist header (double 2×10’s, no hangers) which supports the other end of the floor joists. The header is supported by a 4×6 beam. One end of the beam is sitting on the centre pile and the other is supported by a telepost inside the basement of the original sturcture. There are also 8 inch x 12 inch poured concrete grade beams between each of the piles (not sure if the grade beams are pinned to the piles). Partition walls of concrete blocks sits on the grade beams (between the piles) but do not support the rim joists (2 inch gap to the rim joists). The crawl space is currently unheated and contains the spill material from the piles. There appears to be a poured concrete slab under the spill piles, probably a padio slab existing before the additon was constructed. Local building codes call for footings at least four feet below grade (frost line). I would like to seal the crawl space and heat it and also improve the foundation for a possible second story additon.
The solution I came up with involves replacing the piles and grade beam with a rubble trench foundation complete with a poured concrete footing at grade and a 2×6 PWF foundation wall. I would like to complete the work myself with as little expense as possible and am prepared to hand dig the trench if necessary. I plan to support the structure durring the excavation work with timber supports laid out on the concrete slab. The new foundation wall would be sheeted with PWF plywood, parged with concrete to match the original structure and insulated with fibreglass batts.
I am interested in comments or suggestions regarding the suitability of my solution as well as tips for the construction. I’m particularly interested in knowing whether a rubble trench foundation is suitable for an additon to a struction with a different foundation system.
Replies
You provided a lot of info there so I may have gotten confused a little. It sounds like, if I might sum it up, you have a conglomeration of different stuff, not all of it doing anything and you propose to add to the mess.
You mention that the local code requires that the foundation go to four feet below grade but then propose to replace the existing with a rubble wall placed on a footing at grade level. If that is correct, You would be building a foundation wall subject to frost heaves.
Your floor framing system might be barely adequate, but adding another floor above definitly calls for more.
Assuming (see the little red flag go up?) that your concrete pilings were placed to four feet deep, you could leave them to continue to support the corners while you dig the trench (hand digging is NOT a way to save money IMO) down to four feet or so between the pilings and pour the footer there. If you are looking for a stone wall look, use 12" block to build up to grade level and then lay 6" or 4" block up to the sill and face the outside with stone. You can make the stone disguise the corner posts or chisle them out one at a time as the rest of the wall takes load.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
Thanks for the advice (I did get caught up in description). I should have mentioned that the local code for a foundation wall requires continuos footings a minimum of four feet deep. Code for pile and grade beam system requires 12 inch diameter piles, 12 feet deep on 8 foot centres. I was thinking of cutting the piles off at grade and pouring a proper concrete grade beam over, but the unkown pile depth and wide spacing made that seem too risky. Second option, as suggested by piffin, involed trenching, pouring a concrete footing four feet below grade and building a concrete block foundation wall. The footing and wall system is probably the best option, however I was intrigued by the rubble filled trench system. Does anyone have experience with this type of foudation? As I understand it, this type of foundation involves a continuous concrete footing poured at grade over a trench filled with crushed rock. The trench would be dug to frost line and would include some sort of drainage such as weeping tile and a sump.
inRitchie
That's one you'd have to get approved by your local inspector. My biggest concern would be to keep water out of it. I know you mention drains but if they fail the rubble will act as a sump for groundwater to drain into instead of out of. It will then freeze and heave your concrete and addition up out of the ground. I have a hard time thinking what the advantage is to doing it that way..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit. The second is to look things in the face and know them for what they are." --Marcus Aurelius
Here is a good link for a rubble trench in action.
http://www.daycreek.com/dc/HTML/journal102598.htm