Hanging Joists

Dear DIY'ers

I want to replace a floor that I've just removed, instead of chiseling out the wall and slotting the joists in the holes I would prefer to fit a joist laterally along each side and then hang the new ones within this new frame.

I suppose I should chemical bolt the joists to the wall, my question is how frequently should I place the bolts and what diameter rod should I use?

The floor will be 4.10m x 9.8m and support a bedroom and bathroom (no bath)

The floor finish will probably be 22mm particle board with a resin or 'beton cire' and the ceiling, 10mm timber or 13mm plasterboard.

All suggestions most welcome!



We used 400 centres for joists because the chipboard we bought was 1200m. If you go for 450mm centres, just check your flooring material dimensions......

For the ceiling, 600mm centres worked fine for us and even better if you can separate from the joists above by suspending the counterbattens on metal brackets to minimise noise transmission.

And, of course, pack in as much insulation as you can.

Thanks Chris

Sorry I meant to call you last night.

So you are suggesting 225mm joists at 400 centers as a minimum, I was hoping to use 200mm as I wish to create more headroom in the room above. I could lose it on the ceiling below I suppose. I had planeed to have that a 240cm but 237.5cm would be ok do you think? Or is that staring to get a bit pokey?



Hi James

The answer to your question of chemifix bolts is, used correctly, fixing into good solid stones and also blowing the hole out clean of dust before chemifixing is a must. Another fixing option is to use M12 through bolts, also fixed into the most substantial stone work you can find at an absolute maximum of 1m centers. Also your pole plates should be at least 50 x 225 as should your joists which should be at a max of 400 centers with at least 1 row of staggered noggins down the center. The reason for not using 600 centers is because of load bearings and also chipboard is very flexible and for a proper job on your plasterboard ceiling below it would be highly recommended to counter batton your ceiling at 400 centers. This information is given off 1 photo, no site visit and within current building regs.


Ok I'll go with 450 centers then, what do you reckon with using a resin finish on chipboard. Resinence do a few varieties http://www.resinence.com/prod-Beton_mineral_pour_sols-1-8-44_fr.html

Do you think the resin is a bit flexible, what substrate would you use if we go down this road?



Yeah those holes are a mare to do but it'll be worthwhile. We used 400mm centres and when using tongue and groove chipboard as the floor we went mad with fixing screws (300mm centres) to stop the edges squeaking. Worked pretty well - ragreaged and tiled it and still OK after 2 years. Recommend spending the extra time and money.....

So I'm going to use 75 x 200mm joists at 600mm centers, according to my Roy Chudley and Roger Greeno Building Construction Handbook this will suffice for loads of up to 50kg/m2 if I want up to 125kg/m2 I'll need to do 450mm centers, the difference is about 5 extra joists and about 140€. And 10 more holes :(

snap steve. in fact we replaced one here because of termite damage and poured in concrete. my OH wanted a beautiful wooden floor, insulated and la-di-da. I remembered my house near Cambridge that had originally been a shop built late 18th century where I so desperately tried to keep everything, so did what you did. we could hear our cat! the creaks and groans from the whole upstairs were terrible. in principle kate may be right but then maybe not!

My bigggest regret when we redid this house was just laying wooden floors over the old joists, the floors are horribly noisy. So much so that we later added insulation for acoustic purposes for the two bathrooms and for draft purposes to a cellar under the living room. If we ever do another house, I will seriously study the idea/cost of pouring concrete floors.

In that case Kate, I'll go into the wall, I was hoping not to have to do that but if the end result will be quieter then so be it.



Hi James. Some of it but not all.

Our advice - go into the wall for strength and it'll be a much quieter floor too.

My father and his partner did lots of this when doing London 'warehouse' conversions. They had a guy in an architect's practice who took calcs on. All materials and measurements were taken into account for load distribution and exact use after work was completed, such as what typical furnishing and fitting might be. I remember that many of the base plates or joists they built in were buttressed because fitting new joists into the walls was more work than necessary and sometimes impossible to begin with. Bottom line though, unless you have the civil engineering guidance do not take chances. I have a similar toughie when I am back in shape because one joist that is in bad shape has a 300 litre immersion heater actually part on it and the one beside it that also needs replacement is too close for comfort. Parts of the baseplate are crumbling. I have looked at it with two builders who do restorations and I think we did a lot of head shaking before working out how to do it - which involves the plumber emptying all water, the solar system and supporting the thing from roof joists when it is empty... I am deviously likely to invite a friend who is a retired architect to visit before on the benefit of any doubt.

I've just removed a floor that was dangerously fragile. Had I injured myself on that I wouldn't have considered the previous owner to be liable. In any case I won't be installing anything that isn't up to the job. I'm not new at this :)

Won't the inward force be countered by the joists?

(Realising I am about to sound like a real wimp)

What happens when/if you want to sell the house ? If the people buying don't ask for more info on how sound it is, if you do sell and the floor falls in, how liable will you be ?

Hi James

It's not just the size of the bars or bolts holding the longitudinal beam you need to think about. There'll also be a load trying to pull inwards on the wall.

Can you not put the fixings into the beams that cross the other room?

I think the best way is definitely to go into the wall :(

Steve, I know what you mean, the room looks pretty cool now, if a little disproportionate.

I'm more than happy to take advice on here as I know we have some seriously professional engineers reading this, I'm waiting for them to tell me about bolt shear strength.

I think 15mm diameter rods at 400mm centers and 400mm depth should more than handle it.

Reminds me of when I removed floor from a room here, we liked the look of the result so much we left the floor out and ended up with a dining room with a very high ceiling.

I don't think I'd be happy with putting in a floor like that ( 50m2+ ) based on advice gathered on a forum like this, I'd rather see some proper engineering calculations.