Suspended floor problem?

pertinky · 7 Mar 2019

Hey guys,

I'm in the process of replacing carpet for some hardwood floor in a small lounge. I've just ripped a few of the floorboards up to find a void of about 10-12 inches, some dwarf walls between 1 and 2 courses at 1.5m intervals, and the substrate is made out of 4x2 timbers that are just resting on the walls.

This seems like very poor construction that wouldn't pass regs in a million years. The timber is relatively new, and I know the house was renovated 18 years ago.

My gut feel is I rip it out and start again, maybe installing some 6x2 joists (the voids would prohibit anything larger) but i've never hung them off the wall before.

Is this a big job for a fairly competant DIYer?

bobasd · 7 Mar 2019

why did you lift the floorboards - is there movement in the floor?
if the suspended floor is dodgy in that room check any other suspended floors for similar issues.

through ventilation is needed below suspended floors - do you have enough air bricks?are the dwarf walls honeycombed?
all joist tails an plates must be sat on DPC's.
is the soil dry or damp?

why not post some photos of what ou have?

pertinky · 7 Mar 2019

bobasd said:
why did you lift the floorboards - is there movement in the floor?
if the suspended floor is dodgy in that room check any other suspended floors for similar issues.

through ventilation is needed below suspended floors - do you have enough air bricks?are the dwarf walls honeycombed?
all joist tails an plates must be sat on DPC's.
is the soil dry or damp?

why not post some photos of what ou have?

There is plenty of movement just from us using it daily (2 adults and 2 large dogs so lets call it a small family). I lifted some of the boards to see if it was fixed to the walls, which it is not. It definitely got worse since we use the room quite frequently than I suspect the previous occupants did (we're changing the layout of downstairs so there was a 2nd living room that I think was generally used.

Plenty of ventilation, the room is actually in the center of the house but the adjacent hallway is also suspended and there are air bricks to the front of the building. When the installed the conservatory they've put some soil pipe through to move bricks at the back of the house.

By honeycombed I presume you mean the bricks are sort of staggered to allow airflow between. Yes this is the case and the timber looks in good nick otherwise.

I'll grab a picture of the joist tails. They are on blue bricks I don't think they are sitting on DPC!

pertinky · 7 Mar 2019

WhatsApp Image 2019-03-07 at 13.17.05(1).jpeg

WhatsApp Image 2019-03-07 at 13.17.05.jpeg

bobasd · 7 Mar 2019

if the floors movin then replace it.
joists have to be secure in wall pockets or in hangers pinned to plates/ledgers.
careful liftin of boards an joists means you can re-use them.

post the room dimensions on here - maybe you can span an support without the dwarf walls.this would allow good ventilation.

is ther a chimney breast in the room?

can you post a photo of the external grond level with air bricks?

pertinky · 7 Mar 2019

bobasd said:
if the floors movin then replace it.
joists have to be secure in wall pockets or in hangers pinned to plates/ledgers.
careful liftin of boards an joists means you can re-use them.

post the room dimensions on here - maybe you can span an support without the dwarf walls.this would allow good ventilation.

is ther a chimney breast in the room?

can you post a photo of the external grond level with air bricks?

Room is approx 4m L x 3.2m W (joists running along length

There is a chimney breast ye I won't know how its tied in that end untli I remove some more of the chipboard.

Just been discussing with the missus as the room's running through an opening into the extension thats being done we're going to keep the same flooring (porcelain tiles over screed) running through into this room which means I'm going to need to redo it to minimise deflection, overboard with 18mm ply and maybe 6mm concrete board to bring it level with the extension. That should be adequare with some S1/S2 adhesive.

6x2 definately wont span without support, 8x2 might do though.

pertinky · 7 Mar 2019

Got a few more of the larger chipboard pieces up so I can see. Theres 3 walls so the maximum span using 4x2 is 2m but I guess the grading of this timber is poor for its intended use and is more likely to warp/twist. After doing a bit of research this method of suspending a floor seems reasonable (quality of workmanship is another matter). The wall plate is made of bricks cut in half, some packers and there is no DPC.

I think I would be better replacing them with 6x2 joists and leaving the walls in situ. Span tables for 4x2 are about 2m so I'm right on the limit really. Increasing this to 6x2 will give me plenty of breathing space and a superior quality timber will help too. If theres no regulatory need to fix a ledger plate and hang them off then it would be less work for myself.

bobasd · 7 Mar 2019

using 8" x 2" will make it simple - dwarf walls can be removed an no meeting of joists halfway.

so, existing you have a lip at the door threshold to the extn?
the extn FFL tile is higher than the lounge floor by how much?
solution is to raise the FFL height of the lounge but raising the FFLcould bring other problems.

as i mentioned above, joists must be securely fixed - not just sittin on bricks.

youd do well to post photos of the open floor showin the walls at each end of the 4M & esp. round the c/brest hearth.

pertinky · 8 Mar 2019

bobasd said:
using 8" x 2" will make it simple - dwarf walls can be removed an no meeting of joists halfway.

so, existing you have a lip at the door threshold to the extn?
the extn FFL tile is higher than the lounge floor by how much?
solution is to raise the FFL height of the lounge but raising the FFLcould bring other problems.

as i mentioned above, joists must be securely fixed - not just sittin on bricks.

youd do well to post photos of the open floor showin the walls at each end of the 4M & esp. round the c/brest hearth.

Ye I appreciate 8x2 would render the walls uncessessary but then I'd have to hang them off the internal walls which is more work.

The lip between the rooms is no more than 5mm (screed meets suspended floor) but this can be hidden with the tiles in the opening which means the lip at the other end of the room with the hallway will only be the height of the tile. I'm not concerned about the levels really you wouldn't notice anything.

So in a typical sleeper wall construction there should be a timber wall plate no? and the joists fixed to this. But how is the wall plate secured to the sleeper?

pertinky · 8 Mar 2019

I think im going to struggle with increasing joist size, so maybe bolting some more 4x2's on to it will be the only option...

The problem I can see if where the underfloor heating pipes run into the adjacent rooms the pipework is up against the underside of the joist now, and there is no slack there to put even a 6x2 in its place.

Likewise the hearth is built on blue bricks, and a couple of the joists rest on that so that would have to be altered to accommodate deeper joists.

With the span tables on the limit with 2x4, 4x4 would be enough to reduce deflection comfortably I would have thought.

It's not ideal, I'll need to get some netting tacked undernearth so I can still put 100mm insulation boards down and probably take the time to install DPC and wall plate and make sure its all level (i suspect not)

pertinky · 14 Mar 2019

Finally got around to lifting it all up.

Its not great, and I dont really have the budget to fill it in so I'm going to need to work with it. As you can see im not surprised it was bouncy given half the joists were not even supported by the middle sleeper. Using slate to pack was a bad idea as the bounce has broken alot of it up making the deflection worse.

The sleepers are solid enough although the brick work is sh*t, theres a few loose bricks in one corner where someones just given up or ran out of mortar for the day so I'll need to fix these. Impossible to install wall plate due to UFH pipework and shallow void so I think its better to just leave it be and but run DPC across them before packing new joists with glazing packers and some grip fill.

Is there any issue to me reducing spans to 300mm? Mainly for 2 reasons:

1. Reduce deflection (probably marginally but every little helps)
2. Insulation slabs will cut nicely in half for the voids.

I'll run some noggins across the ends to discourage twisting as well as mid points between the sleepers (as opposed to building 2 more sleepers in between)

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Suspended floor problem?

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