Replace floor joists - Step by step

loveisdivine

After getting a rather eye watering quote for a company to remove the woodworm rotted joists in our spare room and replace with a concrete floor, I've decided to have a look at perhaps replacing it ourselves with new timber joists.

After spending a good bit of time researching on the net, I've come up with the following

Take up floorboards (some are already up from inspecting the joists below)

Remove all current timber joists.

Replace with new timber joists, should I put a woodworm treatment on them before installing? I've been trying to find a good step by step guide for installing the joists but haven't come up with anything really good yet.

I'm not sure if joist hangers are currently being used. Need to check that later.

Where would I buy the new timbers? Obviously not the local DIY shop. Would they need to be ordered from a builders providers?

I already have some instructions for a basic insulation using rock wool between the joists with netting underneath. Sealed with air tight tape.

Also, the current ventilation brick has been rather poorly sealed up on the outside with cement for some stupid reason, so I need to try and open that again and install another vent of some sort.

Any opinions or advice? I'm not gonna rush into anything and want to be sure of the steps and what's involved before undertaking anything.

tabby aspreme

If you pull up more of the old floor you will get a better idea of what you need to do , more than likely there are stub walls 12 to 18 inches high with damp course on top , then you will have something like a 4 ✖1 1/2 on the flat on top of the dpc, the joist run perpendicular to the stub walls , if you replace the timber like for like you should be ok, there should also be several rows of bridging between the joist. If you have stopped the source of the damp you won't need woodworm treatment, if the damp continues the wood will rot irrespective of what you put on the wood, be sure to reopen the vent or put a new one in.

loveisdivine

All that's under the floor is about a 4 foot gap and then bare earth as far as I can currently tell. But I'll pull up more tonight and have a look whats going on.

We believe we've sorted one source of the damp issue. A drain at the front of the house had been left blocked and overflowing for a long time by the previous owners. Since we sorted that, the damp area in the hall (that is in the exact spot the spare room is) has all but dried up. Hopefully sorting out the sub floor ventilation will complete it.

I'll try and get some photos tonight because from what I remember I don't recall seeing any kind of bridging.

Calahonda52

How big is the room?
what is the wall construction?
how old is the house?
am confused with the link between woodworm and damp: i did not realise they were amphibious!
let make sure we are all on the same page here

tabby aspreme

Calahonda52 wrote: »

How big is the room?
what is the wall construction?
how old is the house?
am confused with the link between woodworm and damp: i did not realise they were amphibious!
let make sure we are all on the same page here

Woodworm cannot survive in timber with a moisture content of less than18%, in a well ventilated unheated space such as under a floor, timber would typically have a moisture content of 16% . Woodworm treatment companies don't like people to know about the link with dampness. If you want your woodworm to be amphibious that's ok.

evosteo

can you post pics of your progression

stage by stage

cheers

Calahonda52

tabby aspreme wrote: »

Woodworm cannot survive in timber with a moisture content of less than18%, in a well ventilated unheated space such as under a floor, timber would typically have a moisture content of 16% . Woodworm treatment companies don't like people to know about the link with dampness. If you want your woodworm to be amphibious that's ok.

Thanks for making the explicit connection for the OP

loveisdivine

Didn't get chance to take anything up last night so I'll have a go at the weekend.

I do have some copies of the pictures the surveyor took though. They're not great though.

House originally built in the 70's. If I had to guess I'd say anything that's supposed to be there probably isn't, most stuff in the house seems to have been done incorrectly or only half done.

Room is about 2 metre x 3 metre.




I'm not sure why there's so much ****e on the floor like old wood and stuff.

chris445

Are the joists definitely only in that room?
Do they go under any stud walls etc. that will need to be removed?
If not and its just a single room it should be handy enough.
I doubt they are using joist hangers on a ground floor.
Its most likely dwarf walls with ventilation gaps and a kind of timber wall plate running on top of them.

I would do the following:

Pull up floorboards completely.
Remove joists and wall plates.
Replace DPC and wall plates.
Replace joists and bridging.
Replace floorboards.


When fitting the joists keep them back 10mm from the wall and use a splayed cut so the bottom of the joist is about 15-20mm away from the walls. This means if anything ever falls between the joist and the wall like plaster etc it will drop right down to sub floor level and not bridge between joist end and wall.

loveisdivine

Didn't get chance to look at it this weekend but should hopefully get the floorboards up during the week.

The 2 rooms on either side and the hallway at the front of the room are all concrete floors. I think this doesn't help with the ventilation issue, as even if I uncover the air brick that's there, there's no cross draw for it to go anywhere.

Right2Write

I like working with timber and would contemplate that first as you suggest. But if you think that the ventilation issues etc. are a problem, then concrete it yourself. You'll need to put down a damp proof membrane and insulation, then pour and level the concrete. Depending on whether you want this to be a finished floor or a base for say tiles, you'd need to decide on how well you need to level the concrete. That is, if you lay the tiles in a mortar bed and level this using battens.

loveisdivine

I'd much rather timber. I know this may sound silly but I just prefer the feel of it. I can feel the difference when I walk from the concrete living room, to the timber bedroom. Obviously it's just personal choice.

First option will definitely be timber and improving the ventilation. The room will be a library so hoping to put down a nice deep/dark glossy wood floor.

loveisdivine

Does it matter if there is only 1 air brick for the room? If I install another does it matter that they would both be on the same wall?

loveisdivine

Finally got some decent pictures!

Can't see any kind of bracing between the joists. Looks like it should be a simple enough job, just take it all up and replace with the same. Where do I get floor joists from? I imagine you can't just use the kind of timer you'd get in b&q!

loveisdivine

Decide to sort out the ventilation this weekend.

First pic is the pipe that we could see on the inside. It had been completely concreted over. Order a cap thing for it so will get rid of the rest of the cement when that arrives.

Then found 2 proper air vents along the side of the house. Again both had been cemented over. Cleared them both out so hopefully they will go a long way to prevent in any further damp/woodwork issues.

Next step will be removing the old joists

Right2Write

loveisdivine wrote: »

Then found 2 proper air vents along the side of the house. Again both had been cemented over. Cleared them both out so hopefully they will go a long way to prevent in any further damp/woodwork issues.

Are you sure these vents are blocked? Photos just look like the galvanised slatted grill covers have been rendered into place. Poke through the slats and shine a torch in, should be a 4" pipe there of some sort. Is this blocked?

loveisdivine

Those pics are after we chiselled the cement off! The cement had even been painted over with the same brown as the wall.

I do want to check there's not more cement in the pipes though.

loveisdivine

Took everything up today. Hoping to have the new timber by Thursday so we can't start at the long weekend.

The joists will be 2.4m long and there will be 14 or so of them to fit the length of the room (about 3.6m). Do I need cross bracing for these short lengths?

loveisdivine

Quick question. The DPC in place runs along the dwarf walls and down between those and the actual wall. To be extra sure, can I lay extra doc along the dwarf walls (under the sill plates) and have it come up the wall slightly? I don't know how I'd completely replace whats there as it's built into the wall. So would adding extra in this way suffice?

Another question! The sill plates we removed were not secured to the dwarf wall in anyway. Whats the best way to secure the new sill plates? Is there some kind of bolt we can use in the dwarf wall?

loveisdivine

Resolved the above questions. Have a new damp proof membrane ready to put on the sleeper walls.

Another question, if anybody is still reading this! When we put down insulation, I know it's a mesh under the joists to hold it and the insulation sits between the joists. Do I then need to put anything between the joists/insulation and the chipboard floorboards? I read something about a vapour barrier or breathable membrane but not sure what's suitable in our case.

Right2Write

loveisdivine wrote: »

Resolved the above questions. Have a new damp proof membrane ready to put on the sleeper walls.

Another question, if anybody is still reading this! When we put down insulation, I know it's a mesh under the joists to hold it and the insulation sits between the joists. Do I then need to put anything between the joists/insulation and the chipboard floorboards? I read something about a vapour barrier or breathable membrane but not sure what's suitable in our case.

Dunno. Vapour barrier would be normal in ceilings as you describe but warm, moist air rises towards the roof. You'd think that the ventilation that you're providing for below your floor will deal with any issue of moisture there. I'd defer though to those who know more about this!

loveisdivine

Yeah I've been googling it all morning and can't seem to get a definitive answer.

I read that it's something to do with the warm air in the room, meeting the cold insulation and causing condensation under the floorboards. I don't understand how a vapour barrier stops that happening though. I'll keep searching!

smjm

loveisdivine wrote: »

Resolved the above questions. Have a new damp proof membrane ready to put on the sleeper walls.

Another question, if anybody is still reading this! When we put down insulation, I know it's a mesh under the joists to hold it and the insulation sits between the joists. Do I then need to put anything between the joists/insulation and the chipboard floorboards? I read something about a vapour barrier or breathable membrane but not sure what's suitable in our case.

Video here from someone else doing the same, albeit on an older house:

'Removing, Insulating and Restoring a Suspended Wooden Floor. Part 2 of 3'
https://www.youtube.com/watch?v=OdnQL8GFtHY

Might be of help. Worth expanding and reading the comments on that for some clarification. HTH

loveisdivine

Thanks for that! I was unsure about where to put the vapour barrier because it seemed pointless if I would be nailing through it to fit the chipboard flooring. But they did the same and didn't seem to think it would be a problem once everything was completely laid.

One more question for now. Obviously the ends of the joist sit on and are nailed into the plates on the sleeper walls. But what about the 2 joists that will be on either end of the room, where there are no sleeper walls. Do I need to anchor the 2 end joists directly to the wall? I assume butting them up to the wall and skew nailing them only from one side isn't sufficient?