Downstairs Floor Replacement

[PhillCO2]

Hi all, i'm after a bit of input/advice on replacing my living room floor. I'm an engineer by trade and although not a builder or carpenter my building and carpentry skills are pretty good. I will tell you the plan I have and I would appreciate any comments you guys can give me.

The property is a 1930's ex local authority semi. The living room floor had some quite considerable wood worm and 4 of the floor joists were identified by a surveyor as being quite badly infested and replacement was recomended.

The living room has 12 joist spans at 40mm centres, the room is 3955mm wide in the direction of the joists with a sub-floor wall supporting the joists which is 200mm from the outside wall. The joists are 2 x 4.5 inches. Of the 12 joists 2 are supporting walls above and are not heavily infested. 2 additional spans are actually 4 joists, 2 at each side of the chimney breast, these have very little if any infestation. The joists are built in to the outside walls with no method of removing by sliding out.

My intention is to cut out the 8 existing joists in the main floor area and replace in turn with 47 x 125mm C24 timber with two joists meeting on the subfloor wall for each existing span and sistered at that point with a short piece using 4 M12 BZP coach bolts. The timber will be notched at the wall and ends down to 4.5 inch to suit the existing openings. I intend to use DPM on the wall ends also.

Two of the joists partially supporting walls have more severe rot towards one end, my intention here was to cut out the rotten/infested parts, notch out the brickwork at the side to provide an additional joist slot and sister a length of joist to the side past the rotten sections with M12 bolts at 200mm centres.

I've purchased an amount of a boron powder to spray in solute onto the new and existing retained joist work to protect/treat. I will then be laying new 20x140mm T&G over the top, sprayed with boron solute then sanded and waxed on the top surface.

I appreciate you taking the time to read all that I look forward to any input/comments you can give.

 

[tim00]

Post a diagram indicating rotten joists and dwarf/support walls. Show areas of insect damage.

go under the floor(s) and inspect and probe all the joist tails for damage.

Research this site for massive info on timber and damp, and "woodworm" issues.

 

[PhillCO2]

I've had a surveyor out who has been under the floor and inspected. He indicated that four of the joist ends on the kitchen side wall need replacing (the kitchen has a concrete floor and a retaining wall)
The surveying company were charging an arm and a leg for what is essentially a basic rip and replace. I know the minium I can do is the four heavily damaged joist ends the survey indicated but they also indicated areas of light infestation to be cut out and treated so I decided to do the belt and braces approach and replace every easily replaceable joist span which is over an above their recommendation.
The four joist ends they said should be replaced are pretty much like cinder toffee for 70% of the joist to about 30cm in from the wall. The existing joists were sat on wood blocks and not slate or anything like that which I don't suppose helped them.

I can post a rough diagram if needed for people to be able to advise further but essentially I just want to run my thoughts past you chaps here and see if you can see any issues.

 

[^woody^]

I think you have got the gist of it by the looks of your initial post

Generally, timber in walls at ground level is a bad thing, so if you can use hangers instead then risk of future damp is reduced

Bolts at 200mm centres is excessive. 500mm centres will do, and then if you like knock a few intermediate nails in

Not sure why you need c24 timber, is it due to spans? If so it may be better to use a deeper section as this will then be much more rigid with less bounce. But if you cant, then increase the noggins to stiffen it all up

Make sure you soak everywhere with the chemical , and use tanalised timber for all new stuff

 

[PhillCO2]

I think you have got the gist of it by the looks of your initial post

Generally, timber in walls at ground level is a bad thing, so if you can use hangers instead then risk of future damp is reduced

Bolts at 200mm centres is excessive. 500mm centres will do, and then if you like knock a few intermediate nails in

Not sure why you need c24 timber, is it due to spans? If so it may be better to use a deeper section as this will then be much more rigid with less bounce. But if you cant, then increase the noggins to stiffen it all up

Make sure you soak everywhere with the chemical , and use tanalised timber for all new stuff

I could look into using hangers, my thought was to wrap the new ends in DPM lightly tacked on further back and then sit in the wall, do you think this will suffice instead of hangers?

I will bear the centres in mind I did think they were perhaps a little excessive but I was playing cautious as I didn't know any better. I was advised to use some fixings between the sistered joists also, I forget what they are called but they look like jagged washers.

As for the C24, the joist spans are both around 2m in what will essentially be 47mm x 115mm timber so I could get away with C16 but I read elsewhere someone saying if you can afford C24 to use it anyway. Would you advise saving the extra few quid and sticking to C16 for this span in the joist size I'm using?

I had thought about using tanalised but didn't know if it was required as the existing joists had been in since the 30's and look untreated. I have plenty of the boron chemical, more than enough for the whole house and I intended to remove all the upstairs flooring, treat those joists and the staircase for good measure and replace upstairs floors with chipboard.

Also I struggled to find many places stocking graded tanalised timber in the right measurements to suit the job. Would you advise always sticking with tanalised and can you recommend a timber merchant that does this and delivers nationally?

Is there anything I should be weary of if I have to buy deeper timbers if that's all is available and then cut the ends out to 4.5inch to suit the openings>

Many thanks again for your time

 

[hotrod]

Phil, Howarth timber in Liversedge will sort you out:-

http://www.howarth-timber.co.uk/Branch/11/Bradford.aspx

Get them to pressure treat your C16 in their tanks. It will literally only cost an extra couple of £. Wrap joist ends in DPC, treat any cut ends on site with preseravative etc.

C16 115mm*47mm @ 2m span is fine even @ 600 c/c - no need for C24.

 

[PhillCO2]

Phil, Howarth timber in Liversedge will sort you out:-

http://www.howarth-timber.co.uk/Branch/11/Bradford.aspx

Get them to pressure treat your C16 in their tanks. It will literally only cost an extra couple of £. Wrap joist ends in DPC, treat any cut ends on site with preseravative etc.

C16 115mm*47mm @ 2m span is fine even @ 600 c/c - no need for C24.

Thank you very much I will give them a blast and see what they can do for me.

Thanks to everyone for their input