Cinder block to raise slab


  #1  
Old 02-11-17, 04:07 PM
M
Member
Thread Starter
Join Date: Feb 2017
Posts: 1
Upvotes: 0
Received 0 Upvotes on 0 Posts
Cinder block to raise slab

I'm wanting to add a room to my house. My problem is that the existing slab is slated to ground level. Can you use 16"×16" cinder blocks to lay over concrete in order to add a room?
 
  #2  
Old 02-12-17, 03:14 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 45,659
Received 835 Upvotes on 732 Posts
Welcome to the forums Mark!

What was the original purpose of this slab? How thick/deep is it along the perimeter. To lay block over the concrete it needs to have a suitable footer, most patio slabs do not have a footer.
 
  #3  
Old 02-12-17, 03:17 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 36,607
Upvotes: 0
Received 9 Upvotes on 8 Posts
In addition, can you fill out your profile? We don't know where you are located and that has a lot to do with the answers we can give you. Basically what Marksr said, regarding building on a patio. It can't be done without proper perimeter support.
 
  #4  
Old 02-12-17, 04:07 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
He's in Texas so probably no real frost line worry. Do you mean to use the blocks to support a wood floor or what?
existing slab is slated to ground level
What does that mean?
use 16"×16" cinder blocks
Do you mean 16x16x4 concrete pads or maybe 8x8x16 concrete blocks? (As far as I know cinder blocks aren't that commonly used any more.)
 
  #5  
Old 02-12-17, 06:06 AM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Posts: 27,061
Received 1,910 Upvotes on 1,716 Posts
You can, but it presents some challenges. As mentioned, is a footing needed... is the pad strong enough to support the weight of a structure? With no rebar it could crack under a point load.

4", 6", 8" block are available. The first thing to consider is what your inspector will require for anchoring the sill plate. Will j-bolts into the slugged holes of the blocks be sufficient, or will they require you to epoxy all thread into the pad that will extend through the block and sill plate? (Ask your local inspection office for guidance).

Secondly, will you be insulating that perimeter in any way? If you plan to nail baseboard to framing, the exterior walls will need to be shimmed out over the block perimeter... for instance, you might use a 4" block and sill plate, then shim the studs with 2x2s that extend down over the block, as a nailing surface for drywall and baseboard.

I have also seen rooms (basements) where a 6 or 8" concrete block foundation comes up maybe 4'... or to the bottom of the windows, then there is a shelf created where the exterior wall sits on the outer half of the foundation. A 2x4 wall (half wall) is framed in front of the concrete block wall in order to insulate and run electrical.

Getting the framing and siding up above grade is a good idea, adding one course of block is a good way to do it. Its commonly done on small garages and sheds that are built on pads. But as mentioned, it presents some unique challenges on a house.
 
  #6  
Old 02-21-17, 04:45 PM
G
Member
Join Date: Jul 2014
Location: usa
Posts: 241
Received 0 Upvotes on 0 Posts
existing slab is slated to ground level
What does that mean ^?

no, you can't build an extension on a patio slab if that's what you're asking. You have to jackhammer the slab out on the perimeter and add in a footer and concrete foundation. You could just build basically a non-attached room on the slab and it should be okay depending on how strong the concrete is (if there's rebar etc) but I wouldn't attach it to the house if the extension is built just on a slab. It would sink/rise at different rates as the house, and then cause a roof leak. Or it will just flat out fail and sink in edges, causing all the drywall to crack, roof leak possibly etc.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: