Securing end joists of suspended timber floor

[KatieMcMahon]

Just started the process of replacing the suspended timber floor in one of our bedrooms. It was completely rotten with woodworm, courtesy of the previous owners filling in the air bricks.

We've removed all the old timber, and the dpm from the sleeper wall. Next steps will be putting down the new dpm and then fitting the new joists.

The joists will be skew nailed onto timber wall plates, but here's where I'm a little stuck. How do I fix the 2 end joists? As they are up against the wall, I can only skew nail from one side. I assume this isn't sufficient and they need to be perhaps bolted to the wall as well? Can anyone advise what sort of bolt/nail/screw I should be using to secure these 2 end joists?

 

[benjy_b]

Why skew nail? Why not use joist hangers?

 

[KatieMcMahon]

Using a wall plate and skew nailing seemed adequate and simpler/less hassle then fitting the joist hangers. That's how the previous joists were fitted. It's a very small room, joist span is only 2.4m.

 

[oldbutnotdead]

Sleeve anchors and some packers so the whole joist isn't hard against the wall. These things http://www.toolstation.com/shop/p70962?searchstr=sleeve anchor, 20mm offcuts where you bolt through if the wall is really uneven or damp. Make sure you're going into brick/block rather than a mortar course.

 

[oldbutnotdead]

PS Is your bedroom on the ground floor? Cos airbricks don't prevent woodworm , hopefully you're using treated timber and dipping the cut ends as well for the new joists etc

 

[KatieMcMahon]

Yes ground floor. After a specialist survey we were told that the woodworm problem in that room was likely caused/facilitated by damp timber, which in turn was likely caused by lack of ventilation and excess moisture in the ground from an unchecked overflowing drain. Plus we've now discovered parts of the sleeper wall didn't have a dpm. Obviously we've rectified the drain and vent problems. Timber is pressure treated and once cut we have an additional timber preservative to paint on ourselves.

 

[vinn]

The plate on the sleeper wall sits on a DPC not a DPM.
Best practice is for sleeper walls to be honeycombed to provide through ventilation.
If you bolt a carrier plate to the outer wall(s) - then use a strip of DPC material behind it to protect the wood from possible penetrating damp.

When you say the span is 2.4m do you mean the total span across the room or from the outer wall to the sleeper wall?
Fix a joist hanger at the last joist positions - drop the joist into the hanger and screw through the hanger open side and base to pin the joist in position.

Cover the site surface with a DPM (damp proof membrane) to control moisture rising from the soil.
Best ventilation is through ventilation through the sub-area from one side of the house to the other.

 

[KatieMcMahon]

Sorry got my terms muddled up. It is a dpc we have for under the wall plates.

Maybe I'm also using sleeper wall incorrectly. The span from wall to wall is 2.4m there is no sleeper wall in the middle of this. There are 2 small walls built against the longer outer walls for the wall plates and joists to sit on. I was referring to those small walls as sleeper walls, perhaps incorrectly.

I got this the other day to just put on the floor while we were working in the room, if we were to fix it down properly, would it work as a DPM for the floor? http://www.diy.com/departments/diall-polythene-sheet-l4m-w3m/228548_BQ.prd

 

[oldbutnotdead]

Your dust sheet won't work all that well- it might last 25 years, it might not. Good odds if you drop gravel on it or walk on it you'll puncture it. In the scheme of things, 12 sq m of proper heavyweight DPM isn't going to break the bank- get a full roll, on a job the scale of yours you'll use it all eventually.

 

[tony1851]

Skew-nailing joists is not good practice, regardless of the span.

 

[KatieMcMahon]

Why is that? What are the benefits of hangers, more secure?

 

[KatieMcMahon]

We're using 5x2 timber, so would these be ok? http://www.wickes.co.uk/Wickes-Maxi-Speedy-Joist-Hanger-50x145mm/p/156726

 

[KatieMcMahon]

Oh and, if we did use hangers instead,could I use sleeve anchors to bolt the hangers directly onto the masonry wall? There is a DPC below the level they would be at.

 

[oldbutnotdead]

If you're fixing the joists to bearers on top of your dwarf walls all the fixing is doing is stopping the joists flapping around- the direct bearing on the dwarf wall is resisting gravity. Once you put your nogging in, that'll restrain the joists so they can't twist, the skew nails will stop the joists wandering, job jobbed.

Do make sure that you've got gaps in your dwarf walls so the airbricks will still work- one favourite trap is to have the airbricks above the bottom of the joists but below floorboard- all fine til you stick your insulation in and oops your airbrick is now doing nothing useful.

And yes if you decided to change strategy and not use the inner dwarf walls then you can bolt those particular hangars direct to masonry. It'll be a pain getting them all level (he says speaking from experience but it was a long time ago before SDS drills)

 

[KatieMcMahon]

Thankfully, in this case, we live on a hill and this room is on the lower side, meaning the air bricks are well below where the joists and insulation will be. Also gives us plenty of room to work down there, which makes it easier.

To be honest, the original plan was to just replace it exactly as it was (joists nailed onto timber wall plates which were sat on the dwarf walls, they didn't even have noggins!) but with new timber and improved ventilation. Aside from the rot and woodworm the old set up was actually still very strong. Prior to now the room has been used as a dumping ground for multiple ikea flat packs and about 30 banana boxes of books and dvds. Basically it's had a fair amount of weight on it and was still fine.

I'd like to do whatever is simplest, whilst still being safe and structurally sound. It's no secret that we're novices, which is why I'm open to opinions/suggestions on the best route to go We're in no rush so have plenty of time to plan it out.