DPM under suspended floor

3 Mar 2014
Reaction score
United Kingdom

I'm fitting a ledger board to gable end to hang a suspended floor off in new extension. The other end of joists will be on joist hangers hung from the blocks at other end.

Should I bring the dpm up from under the concrete oversight and behind the ledger board at one side and the joist hangers at the other?

Seems to me this would completely eliminate any risk of damp wood.

Sponsored Links
You could do what you suggest or, perhaps simpler, run lengths of DPC behind any ledgers or plates?

"joist hangers hung from blocks" what does this mean? Hangers would usually be pinned to the ledger board.
Sorry if not clear, I'll try to explain...

Here is the house, with extension planned to the side.

On the current gable, ledger board with joist hangers like this (will it matter if this is below the current dpc on gable?)

On the far side/new gable, hangers set into blocks

Or should I just put a ledger on both sides?

Also can joists span 2.7m with no sleeper?
No, it wont matter if its below the house DPC just so long as it has a strip of PC behind the ledger.

You can hang from a ledger or as in the pic, from the masonry.

Joists can easily free span 2.7m - google joist span tables.
Sponsored Links
On the new side, why are the joists not just built into the wall?

As regard the span; without sleepers, 6x2 would be OK; 5x2...........?
Why not check the span tables?
They could just go in wall, but think in trying to be over careful keeping the wood away from any moisture! I know it will be above dpc so would be an option.

Given that I'm building it myself and I'm not a pro, I imagine a ledger on each side would be the easiest way of getting the floor level? Without having to rely on mm perfect blockwork?
You wouldn't need to have the blockwork so precise. Just leave over-large slots in the blockwork and pack up underneath the joists later to get them level. Then fill the gaps above with foam.

Masonry hangers are not cheap, and you will still need to do a little packing to get the joists seated level.
Thanks Guys for the help.

Getting my head around the floor/dpc seems to have been the most complex part! Just with it being on a slope and all!

I'll abandon the masonry hangers thought then.

Is sitting in the blocks as suggested easier in your opinion than having a ledger on both sides? I've not used foam etc before but have built a couple decks so maybe it just sounds easier to me!

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links