Searched the archives but still unsure…maybe someone could direct me to a link I’m anaware of or advise…
Building 24 x 32′ garage (which will be used as a rec room for next 5 years-insulated and heated) with three bedrooms above. Block frostwall around perimeter (4′ to bottom of footer, I believe here in NE Pennsylvania)Three of the garage walls will be block as they will be backfilled partially(It is in a south facing slope)There will be a 6″ slab, 2″ rigid foam under slab, and 4″ stone under that.
My question is: the builder has dug a trench for the footer, no plans on using forms or building one, can anyone tell me more about the correct way to do this? Rebar? Frostwall secured to footer? Ect. This is new to me.
Thanks,
kb
Replies
personally I don't get trench footings. But that is probably just from having never done them, they are used from what I hear in lots of areas. One question I have is where do you put the drain tile? do you then dig another trench after you've poured?
I like to build footings, but I'm sure you will get some responses from guys who like and use trench footings, and will be able to provide you with some good information about them.
BROWNBAGG is one member who I know is a supporter of them. I had a discussion with him not to long ago in the ' footings or beams thread' (see if you can find it) in the end I don't think he got around to answering some of the questions I had at that time but perhaps someone will now.
Edited 6/12/2005 1:56 pm ET by nails2
bumpignorant and interestededucates me?
Little hard to get the exact picture since you didn't really say how high the walls are to be above grade to the top of the slab. I got the 4' part, but how high above that? You did say it is a sloping site which would lead me to believe that the walls will have some unbalanced fill against them. By "unbalanced fill" I mean the height of the portion of the wall that has fill on one side but not the other.
Will the above floor part of the walls be framed with wood? Or is this a masonry structure?
Re the footers, no nead to form up if your local soil is heavy enough to retain good trenches. I'm sure this sounds a bit strange to some people who live in areas with granular type soil that won't hold it's shape very well, so I'll attach a pic.
Rebar? Depends how stable the soil is at the bottom of the trenches.
Stem wall pinned to footers? Depends on how much unbalanced fill there is. Sometimes a 'keyway' is tooled in the wet concrete footer to keep the block from moving around.
how do you guys do your drain tile?
Location of footer drains? Depends on the soil conditions. No doubt that it's best to put the drains beside the footers, but if the soil is hard clay and you are going to fill both inside and outside the foundation, I don't see the urgency to do all that extra digging, especially if it is gonna put your pipe so low that the drain tail can't be daylighted. Attached is a quick, simplified sketch. We also install a "positive crawlspace drain", which is basically a separate daylighted drain that will drain off any water that could end up under the house. (not shown in pic). The subject garage foundation would be similar. Matt
drain tile, we dont need no stinking drain tile.Honest, we dont use them, we have no need for them. we have no basements, everything is sand. just build the house out of the ground.
Exactly!!! - Soil conditions vary so greatly around the US, Canada, etc, that many of these discussions are just academic - at best. Like the other day when someone said that all clay was not a good footing base. As far as the drain tile, 100 mi southeast of here it the same as you said - just so you have a well drained site.
Matt
Edited 6/12/2005 5:17 pm ET by DIRISHINME
lol...now I finally know. a while back on another thread you suggested I use trench footings, couldn't understand why I wouldn't use em.
turns out, if you lived where I live you wouldn't use em either. need drain tile here. and if I lived where you live I'd be using em probably all the time.
Speaking of footer drains, when the masons finished my block basement they installed the footer drain on top of the footer. The floor into my basement is just above the drain pipe so you see it when you come out the basement door. Doesn't look right, but in my ignorance I'll ask another question.
Is the drain for surface water that has made it's way down to the footer or is it for ground water that has made it's way up? The holes in the pipe are facing down, so if it's for surface water how does the water actually get into the pipe anyway? Just wondering? Seems like it would take an awful lot of water draining down to the footer in order for it to find it's way into the pipe. Mine is daylighted out so I've checked it over the last five years, never even looked damp, haven't ever seen any water coming out of it. Which is good I'm hoping.
In this case, the builder said he would lay the drain on top of the footer. There will be radon pipe in the stone below the slab and exited out the side of the block.
code on footer around here is, three #5. But from a engineer calculation point of view. my house was not heavy enough to need rebar. remember rebar does nothing till a force is applied. The concrete will hold the force just fine.
Edited 6/12/2005 8:12 pm ET by BROWNBAGG
Sounds like your builder has the right idea with respect to the drain tile. Having good drainage relieves possible hydraulic pressure that can be caused water buildup and will results in leaks and other foundation problems. The drain tile is designed to drain off water weather it comes from above or below. Sounds like you have a well drained site too.
BTW - what is "2b"? Understand that grading and classification on gravel products is highly regional too, and sometimes different between two quarries that are 20 miles apart. I think that generally the classifications are set up by state DOTs, and obviously different between NC and PA.
With that much unbalanced fill, we are required to fill the block solid and put rebar in it. It should be pinned to the foundation too. Again, the footers themselves may not need rebar, depending on the soil conditions which none of us can see from here (on the Internet). Assessing soil conditions is something that only comes with expierence, and even then, a soils engineer is sometimes needed.
Personally, with you setup, I'd be very interested in the waterproofing plan. IMO (again, formed by what I know from building in the SE US), after the waterproofing is applied to the outside of the block, it is important to but some kind of drain mat up against the wall to help protect the waterproofing from rocks in the backfill and act as a drainage plane (in addition to the washed stone). Rigid fiberglass insulation sheets are sometimes used and it is quite cost effective. There are other products as well.
BTW - my sis & BIL live in E. Strausburg. I know that PA adopted a statewide building code not too long ago, but I don't think enforcement - which is normally done on a local government level, is very uniform. If you have any specific code questions, they should be posed to a local building official, or at least someone who is very familiar with whatever code PA uses. I saw a code map of the US the other day but can't remember where that was. Matt
I'm not really familiar with stone aggregates but 2b looks to me like clean gravel that they use on most driveways around here. Maybe 1-2" angular type limestone gravel.
The builder plans to "pour and core" the entire North wall. I assume he means rebar every 4' and fill every block with poured concrete once erected. For extra precaution we talked about dampproofing the wall from the footer up with either thoroseal or a membrane of some sort (any one's you'd recommend?)
Then we'd apply 1" rigid foam , then backfill with gravel. We have created a 6' swale behind the north wall that will slope away from the wall and downhill around the finished building to deal with surface runoff above the building.
I never knew building on sloping sites was so much fun!! But the view seem to make it all worthwile.
KB
DIRISHINME, Thnks for info. yeah definnatly bottom of footing, getting it below the slab is I think a priority with the amount of rain we get around here. Yes your inside perimeter drain would eleviate most or all water penetration. And in kb's area he is probably good if that is the common practice for where he lives.
one other question. how do you guys level the concrete as you pour the footing? is it just kinda gravity leveled? how level do you get it? One nice thing about when we build our footings with 2x is that the footing gets staked level. so it's nice having a good level start for starting your form walls. (incedently you wont find much block work around here) anyways, curious to know how you guys work out the leveling aspect
thnks, nails2
in the trench ... drive some stakes... set grade nails in the stakes.. then pour to the grade nailsMike Smith Rhode Island : Design / Build / Repair / Restore
I alway use grade nail stuck into side of dirt wall, lately been using rebar in center of trench driving to grade elevation. Just get a nice six inch slump , and a concrete vibator and float to top of rebar.
mikes way, or your nails into side of dirt sound good. (Mikes might be a bit more accurate)
If the rebar is to be part of the structural make up of the concrete I don't think they'd allow us to drive rebar into ground here. No rebar is allowed ground contact here. (so as not to rust) maybe it's dry where you are and it's allowed there, so I could see that maybe being ok where you are.
In the pic I posted, look closely - you will see the 30p nails pounded in the sides of the trenches - they are spray painted orange to make them easy to see during the pour. IMO this method is a little easier/cheaper than the stobs in the middle of the trench. Also, during the pour, a laser is used to level the wet concrete. The combination of these 2 methods makes for very level footers.
Re your comment about not much block work around here... Here, in NC, we build a lot of crawl space foundations. The reason being that the bottom of our footers only need to be 12" below the finish grade. In your case, in Canada, I imagine that your footers go much deeper - maybe 4'? You are 1/2 the way there already, so you might as well just build a basement... When we build basements, they more often than not are poured concrete. Also, I think in very big cities basements are gaining popularity simply based on the extreme cost of buildiing lots - and the cheap square footage a basement yeild.
Matt
Edited 6/13/2005 6:56 am ET by DIRISHINME
Hopefully I can answer your questions..
The trench is 4' deep by 2' wide. The block is 10"wide 8" high. The garage slab will be 12" above current grade(4"stone,2"insulation,6"concrete)I'm not sure how deep they will pour the footer. Code is 8" I believe but that doesn't seem thick enough to me.
The garage will be bermed into the existing slope. It will be backfilled between 6-' 7' on the north side, from 6-7' sloping down to grade on the west side, exposed on the east side because we are going to put a retaining wall up for a basketball court, and the garage doors will be on the exposed south wall. Therefore the building must be block or concrete. Except the front wall, since it is entirely out of ground we are going to stick build that wall.
On top of the block walls there will be a 12/12 roof with two shed dormers. The soil is mostly clay and shale. Pretty hard at the bottom of the north wall as it is the deepest, we will be backfilling with crushed stone, probably 2B?
I don't think the builder was planning on any rebar, I'm not sure code calls for it. But even so, I'd like to do it right. Opinions?
Thanks for the speedy replies, I appreciate all the input I can get.
KB
kb.... just read all the replies...
sounds like you have a good builder..
lots of guys will trade labor for concrete.. which is what you do when you use a trench footing.... the labor you save, you spend on concrete
... many times the trench footing is more stable that a formed footing..... lot's of uncompacted fill or disturbed earth is under the footing forms.. whereas with a trench... the bottom tends to be undisturbed
i've also done rubble footings where there was deep fill with unsuitable naterial... we dug dep straight sided trenches 10' down thru the unsuitable , uncompacted fill... then dumped 4" tailing stone into the trench until we brought it up to frost depth ( 40" ) then poured our footings on top of the rubble..
Hey Mike... re your last paragraph, we call those engineered footings, and they are not uncommon. I think we are building on more and more of those lots that no one wanted to touch 25 years ago... A few things I don't understand though: It would seem to me that since the downward force exerted by the concrete under a strip footing spreads out at a 45 degree angle (as I understand it), won't some of the load still be transferred To the unsuitable soil? Another thing, it would seem that over time the pressure being exerted downward by the house would cause the rubble (we use #65 washed stone which is basically 3/4" - 1 1/4" blue stone) to migrate outward into the unsuitable soil (muck?) and therefore the whole house would siink a bit? Not trying to second guess your method, as I have used it a number of times accompanied by a stamped letter from a soils engineer - just trying to learn something here.
Do any other of you people have educated opinions on this? Matt
matt.... i only did it once... the trench was about 10' deep before we got to undisturbed earth..
he used a 2' bucket... so figure 26" - 28" of firm material.. and the 4" tailings got a lot of interlock... anyways the 45 deg. would apply if the footing was fluid , right ?
but it's not... it's directing it's force straight down on the rubble tailings... now they can act like a fluid... depending on the interlock...
that was 1984... i was more into seat-of-the-pants engineering in those days.. today , i'd hire a PE and let him tell me..
but the building never moved an inch... and the sidewalks sank 4 " in one place ( over 12' compacted gravel.. so it had to be the unsuitable fill below the gravel )Mike Smith Rhode Island : Design / Build / Repair / Restore
Thanks for the reply and to all other posters as well. I think I can sleep tonight now. They'll be here in the early morning tomorrow to pour. This is a great resource for us perfectionist homeowners/DIYers. Again thanks for the great input.
KB