footers

MELOC · #1 09/26/05, 01:49 PM

hi all, first time so bear with me.
i would like to know what is the proper configuration of footers in relation to the "frostline". i will be building a concrete porch on walls of block or cement and eventually encase it with fieldstone from my property. it seems we are blessed here to have some ice age glacial deposits of many types of stone mainly limestone, quartzite and sandstone.

there are no specific regulations in my area for this. i was told as long as it is below the frostline all is well. i believe the frostline is about 18 inches here in south central pennsylvania. so how deep should the ditch be? how much gravel depth and how much concrete? i have heard non-specifically 2 feet. i have @ seventy feet linear of porch to build, and with a 2 foot wide footer the amount of concrete could be vast. i do not want to go "over-kill" and blow the budget.

should the concrete itself start below the frostline or just the gravel? please help me i am a rookie, lol.

TnAndy · #2 09/26/05, 02:07 PM

"Generally", assuming you have stable soil, the footer should be about twice the width of the wall on top, and as thick as the wall So an 8" wall takes a 16"wide by 8" thick footer. Figure you total wall ( block + stone ) and double that. You also have to take into account whats going on top the wall.....IF it's going to be a 3 story building, personally, I'd go wider with the footer.....a porch or a single story, ( in good, undisturbed soil ), I'd be OK with the 2x rule of thumb.

2-3 pcs of #4 or #5 rebar is a good idea as well.....if your footer does crack, the rebar can save you.

I have never used gravel below footers.....always poured them directly on the ground in the trench. The bottom of you concrete should be below frost line......and on GOOD SOLID DIRT ( did I mention that ...ahahahaha )

WindowOrMirror · #3 09/26/05, 02:40 PM

Good advice already. Make sure that CONCRETE is below the frost line and that you use rebar, The theory is this: If the frost heaves to top of the wall, there's a section on the bottom that WON'T heave holding things down/ In order for this to work, the footer and the wall have to be affixed securely one to the other (rebar).

How deep and wide the footer is will be calculated based on how much weight it has to support and what type of soil you have. Clay soils have a far worse weight-bearing capacity per square foot than do other soils (would require a larger footer).

For a porch, 2x could work in decent, well-tamped soil.

Put the footer below a "worst case" frostline. Here, our frostline is listed at 42"-48" depending on the publication. The median frostline is more like 36". Putting the barn in this winter, I put the concrete beneath the posts at 60"

R

stanb999 · #4 09/26/05, 05:27 PM

Quote:

Originally Posted by MELOC

hi all, first time so bear with me.
i would like to know what is the proper configuration of footers in relation to the "frostline". i will be building a concrete porch on walls of block or cement and eventually encase it with fieldstone from my property. it seems we are blessed here to have some ice age glacial deposits of many types of stone mainly limestone, quartzite and sandstone.

there are no specific regulations in my area for this. i was told as long as it is below the frostline all is well. i believe the frostline is about 18 inches here in south central pennsylvania. so how deep should the ditch be? how much gravel depth and how much concrete? i have heard non-specifically 2 feet. i have @ seventy feet linear of porch to build, and with a 2 foot wide footer the amount of concrete could be vast. i do not want to go "over-kill" and blow the budget.

should the concrete itself start below the frostline or just the gravel? please help me i am a rookie, lol.

First I'd recheck on the frost depth in you area. I do Construction Inspection for a living and can tell you in Lancaster and Delaware Co's the frost depth is 30". I've worked as far south as you can go in PA. and they always specify 30". The thing to realize with possible frost Depth is yes it is "warmer" in the southern reaches of PA but the snow that protects the ground "UPNORT" dosn't stay in the south so the ground freezes to about the same depth. In most years the 24" you propose will probably be ok but that 1 cold year can cause alot of damage.

Questions ?
Is this a deck/Porch or Is this a structure that has to have a continous footing?

What is being used for the structeral members/unsupported Spans?

Is this to have a roof attached to the primary roof structure?

Look into the fact that PA now has ICC codes.

A little more info I might be able to help you.

stanb999 · #5 09/26/05, 05:44 PM

Also what I ment by spans is it may be possible to make piers at full depth and fill the void with stone and build a concrete beam of sorts starting just below grade to support the structure above. This would require more reinforcing but less concrete. You could also look into getting "old" concrete from a ready mix co. They sometimes have leftover concrete from bigger jobs that they must just get rid of. They will have added water so the strength won't be as high but lets face it theirs lots of structures built on "weak" concrete. The strength will be 1500-2000 PSI instead of the 3000 as delivered. But if you get it cheap it will be fine. Maybe they will even have a failed load from State work. If you are flexable with the delivery times You would be suprised at what you can get.

rzrubek · #6 09/26/05, 06:06 PM

All I can offer is this link http://www.construction-resource.com/forum/
Should be able to find some help there.

MELOC · #7 09/26/05, 07:41 PM

about the new codes in pa

i am aware about the new codes in pa but i am not familiar with them. i got a building permit from my municipality but they did not seem overly concerned by the footing question i posed.

the porch will be a poured concrete cap over a fill (gravel and whatever else i can bury that won't rot) the fill is to be enclosed by either block or concrete walls. i have been talked into concrete walls by the family although i was gonna go with block and include my casing anchors as i went along between the block joints.

the porch will have posts on the front on the concrete deck and be supported at the rear by the dwelling. there will never be construction on top of the porch roof.

the casing will be made most likely from the smaller pieces of rubble stone left from the original stone pillars from the old porch. the square stones are for landscaping the flower beds

(by the way, i had 25-30 feet of double row stone walls from two earlier porches that were buried and unknown beneath the old porch, what a find! if time were not a concern i would have rebuilt them in some way along the front maybe or as pillars with a wooden deck)

the cap will most likely be poured in two or three sections as my workforce is limited. i think 70 linear feet is too much for two people all at once. and here i have other questions to friendly ears. i am considering finishing the cap with textured templates and or coloring. any experience in this will be met with open ears and a thick head, lol. i am concerned by the amount of help i will need to accomplish this when the pour happens

time is of the essence. this old wooden porch was devastated by the great wind storm of the mid 1990's and has to be up this fall or i am dis-owned, lol.

stanb999 · #8 09/26/05, 08:31 PM

I see the need for speed.....

I'd excavate to a proper depth. Use Wood to make a form for your foundation wall. Fill with the stone you mentioned and concrete. This is for the areas between the posts for the roof. At the areas where the posts are to be. make it solid concrete at least 8"x8"xfull depth with (4) #4 bars about 24" long spaced in a 4"X4" square pushed into the concrete. Use a 12" piece of galvinized 9/16" All Tread with a nut and washer at the bottom to bolt the post for the porch roof when it is finished. This should be placed into the concrete between the rebar so 2" sticks out. Then I'd suggest you get stone to infill the porch area (but if you use soil put some 6 mil plastic down. Then use 1 layer of concrete mesh place it in the botton 2/3's of the slab. The rebar and mesh placment is critical to the log term performance. The rebar and mesh can be bought at Lowes or Depot.

You also asked about the finishes available. They look great when professionally done. But if I were you I'd first practice away from the house or better yet help your Brother inlaw do his first.