Repairing possible damage to floor joists

25 Apr 2008
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United Kingdom
Hello - I have owned a 1930s Edwardian semi-detached house for about eight months. It is a very standard layout: when you walk in the front door, the stairs go up to the first floor along the outside wall, the corridor next to the stairs goes back to the kitchen, and the front and rear lounge are off to one side.

The house still has its original floorboards. There is a substantial crawl space under the house (2ft under the corridor and stairs portion, deepening to 4ft under the lounges), but this crawl space is tricky to access - you have to go under the stairs and the hatch is tight.

When I first moved into the house, I noticed that some of the floorboards at the base of the stairs felt a bit bouncy - they make noise when you walk on top of them (I can only describe it as a sort of "banging" or a "crunching" noise) and they don't feel 100% sturdy - not ready to collapse, but not rock-solid either.

I have two goals with the house: I want to insulate the ground floor from underneath and I want to put in a new floor. The couple up the street (identical house) actually just put another layer of flooring right on top of the old, original floorboard and I might give this a shot, too.

The other day I finally got into the crawl space and inspected the joists that were making the funny noises. I saw what looked like water damage (there was a wavy line of discolouration, kind of silvery on the wood) probably about 18in or so long on three or four of the joists. There must have been a leak or a flood at some time in the past. From knocking on the joists, however, they don't feel rotten. They feel as sturdy as ever, but they sound a bit dodgy when trodden upon.

Thanks for getting through all of this! Here's my question: I've read in several cases how people have just reinforced the joists by bolting supplementary joists to both sides of the ones that are already there.

Is this solution practical and straightforward to do? Will these additional joists not be too heavy? Should I get a professional in to do this or is it easy enough to do on one's own? If the surveyor neglected to pick this up (I paid for a full structural survey), would I have cause to raise a legal case against him?

Many thanks and kind regards
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a 1930s Edwardian
??? ('Georgian' surely!)

It is possible to reinforce joists by fixing additional joists (aka 'sistering') to the sides. What length you need depends on the span of the joist and how far along the suspect length is.
However, you need to be absolutely sure that any dampness is eliminated, and existing timbers properly treated.
If the suspect joists are only in the hall, would it not be easier for you to take up the floorboards there and just replace the joists complete. Presumably the span won't be very much.
a 1930s Edwardian
??? ('Georgian' surely!)
From wikipedia: Georgian is way earlier


I did know that Georgian was earlier; years ago I used to teach architecture history at University level, and actually specialized in the eighteenth- and early nineteenth centuries.
Notice that I put Georgian in parentheses, hoping that it would be seen as alluding to George V, but my attempt at a little light humour has obviously gone a bit flat!
cheers, tony.
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the crunching might be where they are loose in the brickwork.

I think you are going to have to take up the floor and examine more thoughly.

If it is the original square-edged boards with no T&G this might not be too difficult.
Ah! I see, "pun" understood now.

Blame my "not-from-around-here-originally-but-always-interested-in-architecture-style-periods-but-not-in-kings-or-queens"

Guessing - without seeing a picture of his house - it could be '1930's style ;)
Thanks everyone for the replies.

Didn't mean to launch a debate on Edwardian/Georgian/etc. style! Mine is just a bog-standard, inter-war semi-detached house of which there are millions all over the country. Very standard style. For what it's worth, I think it was actually finished during the reign of Edward VIII (that would be 1936)!

the crunching might be where they are loose in the brickwork.

I think you are going to have to take up the floor and examine more thoughly.

If it is the original square-edged boards with no T&G this might not be too difficult.
You might be right. I should say it's not so much a crunching sound as it is just banging on the joist. You can hear every step and it feels like the floorboards are somehow loose on top of the joist, although there is evidence of the previous owners having nailed them down pretty tightly. I could try to screw the floorboards to the joist from underneath but I really, strongly suspect the joist itself is somehow damaged.

The floorboards are unfortunately T&G so getting them up could be a bit of a challenge.

I should point out that, like most houses built before WWII, the floorboards sit right on top of the joist, which are exposed to the crawl space below. There is no subfloor and no other layer. Just wood on wood and that's it. This is the original floor and the original joistwork.

I will have another look via the crawlspace at the joists from the underside later today and hopefully post a picture or two; maybe someone can help me figure out if it needs a specialist. Ideally I'd like to avoid too much work; I think I can just about handle bolting sisterboards to each of the joists but anything more complicated than this might be out of my league.

take the floorboards up and everything will become far far easier. Even if they are T&G, once you have the first one up, the rest will be easy. You can use a garden spade to lift all but the first one.

when you refix, use countersunk screws (into pilot holes) from above. You can make yourself a bigger access hatch for the future, too.

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