Extension floor bouncing. Can I do this?

[Tony Tiler]

My 30 year old extension of dining room / kitchen has a very slight bounce in it. I think the span of joist (12 feet) is probably too long and I want to put some peers below. Would there be any problems with cutting some lengths of wood with maybe a section out of the end (to stop it moving) and wedging this between joist and floor? Obviously I'd put some damp proofing membrane between floor (which is concrete and bone dry) and the joist.

I know the preferred method would be to build brick piers and wedge these under the joists but I can't help thinking the wooden wedges would be awful lot easier. Plus I am having a new kitchen fitted next week and time is of the essence!!

[Frank Erskine]

John Prescott would be a good idea... :-)

[Tabby]

you could, but there are much better options

NT

[Dave Liquorice]

How tall do these "peers" need to be?

Double wedges will work up to a couple of inches no bother and be adjustable on fitting. Cut lengths of timber will either need faffing about with packing or have double wedges...

Or suitable building blocks (not lego!) with double wedges on slate?

DPM membrane isn't that good a dealing with hard rough surfaces or small stones etc, it's likely to get a hole in it.

[Skipweasel]

Probably fine - after all, the worst that could happen would be it'd fall over and you'd be no worse than if you hadn't bothered.

Three bits of wood to make an A-frame would be less likely to fall out - though you haven't said how high the floor is from the sub.

[Dave]

But wouldn't that make the floor very noisy?

Dave

[Tim Watts]

Dave ( [e-mail]) wibbled on Friday 18 February 2011 21:46:

But you'd be able to tap the subspace void for an everlasting supply of natural gas - save a fortune in heating.

Pie related expenditure might be a problem though...

[Tim Watts]

Dave Liquorice ( [e-mail]) wibbled on Friday 18 February 2011 21:35:

DPC rather than DPM would be better (comes on rolls) - it is very tough. Unles the concrete is full of jagged aggregate, it ought to be OK. Can always double it up.

Another option is metal pads - 1mm ali would be fine.

[Tony Tiler]

The piers would only be about 12inches

Yeah I thought it might not be that great but I could put some wood on the subfloor or some ties before wedging the DPM / wood in.

[Tony Tiler]

That was the reason behind it. If it failed then I'm no worse off. I was thinking if I cut a slot out the part that meets the joist then put a couple of screws right through the lot then the chances of them slipping are slim.

About 12 inches.

[Tony Tiler]

Ideally masonry is the answer but I don't think I would be able to wedge in masonry any where near as tight as wood which really defeats the purpose :o(

[Tony Tiler]

^^^^ Sorry that was meant to say tiles.

[sm_jamieson]

I'd build masonry piers of some time and wedge in some slate or something. Would last better than timber. Simon.

[Skipweasel]

Oh, well, down the breakers yard and come home with a few old car-jacks. Cheap, easy to adjust, nice and tight, plenty durable.

[Roger Mills]

Just wait for the House of Lords reform - there'll be plenty going spare!

Seriously, why not go down the scrappy and get a few bottle jacks (of the screw rather than hydraulic variety). Stand each one on a couple of bricks, engage the stirrup on the underside of a joist and wind it up a bit until it starts to support the joist. They can be re-adjusted periodically if necessary (provided they haven't rusted solid!).

[Tony Tiler]

Not such a crazy idea, as I had thought I would jack up the joist ever so slightly before wedging in the wood.

I must have around 15 joists. Anyone know if I should be doing every one or can get away with every 2nd or 3rd one?

[<me9]

Put a couple of bricks on the subfloor below each joist, then a bit of DPC, then double wedges (nailed once adjusted). This keeps any rottable materials above where any water may persist.

[Tabby]

A breeze block'd be better

If there are noggings, just one little pier may be enough, if not maybe 2 or 3. If no noggings, you'll need a fair few such piers, either one every joist, or maybe one every other joist.

NT

[cynic]

You really ought to support them all. Think about installing a cross member under the present joists then space some concrete/breeze blocks or bricks under the cross member. If the sub floor is smooth(ish) lay dpm on it and the breeze block on top of it, or if rough lay the dpm on top of the blocks, then pack up to the underside of the cross member. Use an incompressible packing such as slate or stone slips.

[damduck-egg]

You can get plastic supports that are intended to support decks,flagstones etc on flat roofs clear of the actual roof. There are adjustable in height with built in screw thread. They are normally fairly expensive but I've just bought a few of a chap on ebay who has got a load to get rid of at . £20 for 10 + delivery if you cannot collect yourself.

them reasonably fast to me.

G.Harman