Replacing floor joists ...

[af7]

Hi!

I'll post some pictures this weekend while I finish up detailed what I have to work with.

Essentially, a 3.2m x 4.1m rear kitchen that I want to rebuild. I've gutted it ... all of the units / plaster (except the original plaster coving) / rotted flooring ... etc... except for the joists.

With open the chimney breast and install a concrete lintel at 2m high and 1m wide for a gas cooker.

It seems that the joists have been replaced previously with 50x100 (2 x 4) and a sleeper wall installed in the middle of the room (1.6m to each wall). It also seems that cavity walls are probably full and the original DPC might be shot (based on what we found upstairs.) The replacement joists sit go wall to wall and sit on top of that sleeper wall.

Based on newspaper found in the wall, I think it was done in 1989.

Anyway, I want to replace the joists with new 50 x 100, which is within building regs (1.6m span, 400 spacing).

What's the best way to replace them?

This is what I can come up with (and possible problems):

1. Use hold in wall and install a new DPC in the wall. Seems that they'll rot again.

2. Wall hangers. Good idea but seems that they'll come out of the same and will be a PITA to level.

3. Sleeper wall next to the main wall? Don't touch the wall with anything? Seems arduous.

4. Wooden wall plate with DPC in between? Could cause a problem in the long run.

I'll get more detail ... took about 3000 kg out last weekend ... old plaster, about 200 bricks under the floor and shoveled all the dirt out.

Will address airbricks and other problems shortly.

Many thanks for your help!

 

[oldbutnotdead]

I'd go option 3 or 4- 4 if the walls are in decent condition. Is the subfloor soil or finished? 2 will as you said be a pain- masonry joist hangers really work when they're built into the wall, if you have to bolt them to the wall you're better off bolting treated 4 x 2 to the wall then fix your hangers to that

How old is the place- is it lime mortar or cement? What's the outside ground level like?- if you can get that down to subfloor level the damp problems should go away. Up to you if you want to try one of the DIY injection DPCs, from personal experience they seem to work but that may just be from sorting the gutters and outside ground level, hard to tell

EDIT. Timber-wise yes 4 x 2 on 1600 at 400 centres is an acceptable minimum. If you've got the depth, use 6 x 2, will give you a firmer floor and space on the face to run batten to hold the insulation (which you will have to fit) up.

 

[af7]

Hi ... thanks for the info ... current photos are here:

https://imgur.com/a/pZiir

If this is impolite and I should upload another way could you let me know

Soil ... shoveled about 1000 kg out to clear the passageways. Originally built in 1909. Lime mortar ... sand and cement on the wall. Am thinking of:

1. removing all the bricks on the outside walls and hovering out the cavities.
2. checking out the original slate DPC and replacing with some vinyl-type stuff or an injection
3. check of the pipes going into the main drain behind the chimney breast ... running some in-ground galleyways to the drain to ensure that it drains off the house
4. remove the outside render from the ground
5. install airbricks in the inner wall and the previous people only did it on the outer wall.

So, installing a treated 50x100 to the wall with a vinyl DPC and the joist hangers from there?

We have space for 50x150 if using a hanger.

However, we're not sold on the insulation as the natural products have been said to reek of a farm if they get damp (sheep wool) and the Celotex stuff seems to be PIC which is what was on Grenfell.

https://en.wikipedia.org/wiki/Polyisocyanurate

Many thanks for the reponses.

 

[af7]

Also, had the gutter problem on the front of the house and it flowed under the main room. So, we'll take care of waterflow/standing water first!

 

[oldbutnotdead]

Best way to do pics is within this site- when you're creating a post you'll see a button marked Upload a File- follow that & you can embed images in your posts which makes life much easier.

Not easy to tell from the pics but 99% certain you've got solid walls. Have a look at the full brick walls (the ones that are 2 skins thick) and see if there's a soldier course every 7 or so courses. If so then raking out the cavities isn't a waste of time but may not be worth the effort.

Inserting a physical damp course in the wall means (if you think about it) making a hole the full thickness of the wall and at least 1 brick deep, inserting your barrier then filling the hole with something structural (bricks and mortar). Which runs the risk of destabilising the whole house. If the outside sand/cement is going to ground level then def chop it back up to at least 300mm above ground. Get outside ground level down to subfloor (or below floor level anyway), inject if you want (make sure you get cream designed for lime mortar rather than Portland cement) and take it from there.

Airbricks in the inner skin- yes that'll be of much more benefit than trying to put a DPC in the wall.

Pipes behind the chimney breast? Can't see them. If they're in good nick then leave them, if they're in poor condition then replace them, maybe move them to somewhere where they can be got at in the future. Pipework shouldn't be designed to leak (which is what it sounds like you're planning with the gulleys)

If you're going to use treated 50 x 150 for the joists you'll find it easier having a treated 50 x 150 wallplate (yes with DPM/DPC between it and the wall).

You don't have a choice about insulating the floor (under building regs)- what you use is up to you but you have to achieve a U value of 0.25. Point taken re PIR but the risk in a standard dwelling is rather low- under the floor is not a likely place for a fire to start, even less likely if the wiring and pipework has been replaced to modern standards. By using 6 x 2 timbers you will give yourself the option of using rockwool (150mm IIRC) instead of Celotex etc (100mm), though you'll need to net or batten under the joists to keep the stuff in place. And it won't get damp cos your new airbricks and cleared floor void will maintain air circulation

PS Your existing dwarf wall looks like a stack of bricks rather than a wall, be prepared for it to fall over if you look at it funny. Then rebuild it with plenty of gaps in it. For that depth I'd do a course of blocks with 200mm gaps between each block then a strip of DPC and a length of 4 x 2 sat flat on the top (to bridge the gaps) for the joists to sit on.

 

[af7]

Hi and many thanks for the advice.

The outer walls are cavity wall ... the party wall doesn't have that ... I guess I should have stated that it's a Victorian midterrace.

I haven't ever seen the soldier bricks on the other walls ... took the plaster off in two bedrooms as well ... only above the original fireplace openings.

Thanks for the advice on the outside render removal ... ground level ... airbricks in the inner wall (desperately needed) and looking at the pipes (outside of the house ... all of the pipes run to that single place on the outer wall behind the chimney breast)

. That will possibly solve most damp problems.

Some a-hole before removed a row on bricks in the inner wall and replaced it with a 50x100 and laid the joist on top of that (left of the chimney breast). So it's embedded into the wall and totally rotted. That's why I was thinking of the DPC in the wall and there's going to be a huge gap anyway.

I'll take a look at the rock wool options.

Thanks for the info about the 50 x 150 on the wall as well.

1. What's the best way to mount the wallplate to the wall?

2. The dwarf is better than I expected except for some mortar issues (which is why I took that photo) ... actually there's quite a bit of mortar issues in the room. They laid bricks the long-way against each other and then stacked and mortared 3-4 bricks up with DPM and the 2x4 is still not rotted on the top. Is this the right way?

3. Any ideas about why the chimney rear hearth would be damp? I'll break it out anyways down the original bricks.

Again thanks for the input. I'll try to get the basics done ASAP (damp and such).

 

[af7]

final 4 photos (sorry for the hassle):

 

[oldbutnotdead]

Fixing the wall plate to the wall- drill and fix with a few 4" screws to start with (to get it into position). Once you've marked where your joists are going to go, pick spots between the joists and ideally into a full brick and use sleeve bolts or through bolts (these sort of things https://www.toolstation.com/shop/Screws+&+Fixings/d90/Steel+Anchors/sd2040/Through+Bolt/p87294 ), best having them at 400 centres or so

Dwarf wall tend to be thrown in rapidly (no-one is going to see it so who cares), if the height is right and the timber hasn't rotted then happy days, not really critical which way round the bricks are, they probably laid the bricks that way cos that was the easiest way to get the correct height. DPM under the timber will stop any damp in the ground/bricks percolating up, airflow will remove any other problems

Damp hearth- it'll be 50mm of concrete or something on top of earth, of course it'll be damp. If you're keeping the chimney as a fireplace then dig out the hearth and the earth down to foundation level (or subfloor anyway) then put DPM on the ground and up the sides and fill with concrete to finished floor level (or -50 and put some paving slabs or something on top to make it look pretty). Back wall of the chimney is probably damp- high internal ground level will do that, if it is a party wall then you'll have some damp coming through from the other side (if their fireplace is in the same place) unless they've got a fire in it. EDIT Unless I've read it wrong you've got pipework and outside behind that chimney. If it is the old cast iron stack going into a clay gulley then its good odds the clay gulley will have cracked (general movement of the building and any nearby bomb impacts from WW2) & will be causing some damp.

Your timber in the wall- beware, you may find it isn't totally rotten (as in part of it may still be carrying load). Dig it out and replace with bricks & mortar in 500mm lengths, put DPC in while you're at it (modern plastic or slate and engineering bricks, up to you).

 

[af7]

Thanks again for the tips. I'll be doing some serious inspections this weekend inside and outside of the room. Last weekend was 3 days of getting everything out.

 

[Footsoldier888]

Thanks for the pics and best of luck for the rest of it.

 

[af7]

Well. I found a major source of damp on an external wall.

I emptied the debris out from the chimney hearth front/rear and started taking bricks out to the right of the breast.

Thick black much about 1m tall was filling the cavities. I think this is due to ground level and water draining off the gutter (maybe with dirt and mad mortar on the outer wall.) Essentially, the ground on the outside is around 10 to 30cm higher than the floor and I believe when it rains the water works it's way in between the mortar in the outer wall and leave muck that it's carrying inside. A simple French drain along the wall of the house would sort this and I'm surprised more houses don't have drain away abilities.

That chimney had quite a bit of debris inside of it.

Do I need to refill it or can I run joists all the way to the rear wall of it? Or both?

 

[JohnD]

I've had something similar in a solid-walled house.

In mine, there was a 4" brick sleeper wall just inside the external walls, with the joists standing on it and extending almost, but not touching, the external wall. The floorboards also did not touch the external wall, but the skirtings hid the small gap.

In my case, the gap between the two walls was largely filled with mortar snots, sand and builders rubble. I cleaned it out by raking and using a canister vac, and the internal wall dried out nicely. I also cleaned out the airbricks, had damp been worse, I might have added more, and later dug out and re-pointed the external face of the wall, re-rendering with a break over the slate dpc to prevent water creeping up it.

In my case the sleeper wall also had slate DPC, otherwise I might have wrapped the joist ends or jacked them up and slipped plastic DPC under them.

I wouldn't let your new joists touch a wall that might become damp, but you can buy a roll of DPC and tack it round them. If they've previously been wet, cut off all affected timber. Treat generously with wood preserver.

 

[oldbutnotdead]

You can do either, depends on your plans for the chimney. If you're keeping the chimney I'd suggest chucking a concrete (or otherwise solid) hearth in, would give you the option of a woodburner if you felt the urge. Once you drop the outside ground level the brickwork will start to dry out, it'll take 6 months or so but if you went the timber route a bit of DPM behind the wall plate would do the job