Strengthening first floor joists

Nolic

The back of my house by the looks of the neighbours must have been a crawl space originally but was converted into another bedroom by adding a dormer window.

But the floor is quite bouncy. I lifted the carpet and floorboards and noticed why. The span is 3.3m. The joist size is 5"x2" which I know isn't strong enough. They then added a 2"x2" on top running the opposite direction to bring up the floor level to match the rest of the upstairs.

What can or should I do to strengthen this room? It's quite bouncy and squeaky.

I've young kids who love to bounce on the bed and don't understand when I ask them not to do it in that room. I'd be afraid they'd eventually come through the ceiling into the kitchen (exaggeration I know).

Any ideas? I can get to the floor joists from above easily enough and would be able to below but would prefer not to if possible as it's in the kitchen.

tabby aspreme

What type of floor is under the carpet

maestroamado

I think if you nailed the 2" directly on top of the joist and nail about every foot, put good quality 3/4 plywood on top it would work, also add plenty of soundproofing.
Good quality t&g floorboards do the same but they need be 3/4" to 1".

SC024

Nolic wrote: »

The back of my house by the looks of the neighbours must have been a crawl space originally but was converted into another bedroom by adding a dormer window.

But the floor is quite bouncy. I lifted the carpet and floorboards and noticed why. The span is 3.3m. The joist size is 5"x2" which I know isn't strong enough. They then added a 2"x2" on top running the opposite direction to bring up the floor level to match the rest of the upstairs.

What can or should I do to strengthen this room? It's quite bouncy and squeaky.

I've young kids who love to bounce on the bed and don't understand when I ask them not to do it in that room. I'd be afraid they'd eventually come through the ceiling into the kitchen (exaggeration I know).

Any ideas? I can get to the floor joists from above easily enough and would be able to below but would prefer not to if possible as it's in the kitchen.

is there bridging fitted? should be 7 x 2s by right,

maestroamado

SC024 wrote: »

is there bridging fitted? should be 7 x 2s by right,

Your right adding 7" bridging to what i said be big advantage as binds everything.
There is no reason why this not work...

Nolic

tabby aspreme wrote: »

What type of floor is under the carpet

Tongue and groove timber floorboards

Nolic

SC024 wrote: »

is there bridging fitted? should be 7 x 2s by right,

There's no bridging

Nolic

maestroamado wrote: »

Your right adding 7" bridging to what i said be big advantage as binds everything.
There is no reason why this not work...

Thanks a million for your help. I appreciate it. Should I prop up underneath also?

sydthebeat

Nolic wrote: »

There's no bridging

that is singularly the main reason there is so much bouncing.

at a span of 3.3 meters you should put in 3 rows of solid bridging at 800mm centers.

if you are taking up the floor boards, id also take up those existing 2 x 2's.

replace them with new 2x2's (or reuse if in good condition) directly over the existing joists. This will allow you to use stronger 7 x 2 solid bridging pieces.

you should put down 18mm Brazilian hardwood plywood as the floor covering and dont skim with the screwing.... go through the new 2x2s into the joists, so look at using min 4" screws (probably use 6 x 120s)

sydthebeat

Nolic wrote: »

Thanks a million for your help. I appreciate it. Should I prop up underneath also?

you should only prop underneath if there is a visible bow on the existing ceiling.

Nolic

sydthebeat wrote: »

you should only prop underneath if there is a visible bow on the existing ceiling.

There isn't a bow when looking at the kitchen ceiling but there's probably an inch in it up stairs when you've a level on it. Thanks a million, I really appreciate all your help.

Was looking to get someone in but wanted to see if I could do it myself to save on cash as I don't have the funds for it.

sydthebeat

Nolic wrote: »

There isn't a bow when looking at the kitchen ceiling but there's probably an inch in it up stairs when you've a level on it. Thanks a million, I really appreciate all your help.

Was looking to get someone in but wanted to see if I could do it myself to save on cash as I don't have the funds for it.

you might not see an inch bow from below without using some kind of laser level

if its obvious above then id prop anyway, be very careful rising the bow though.

Calahonda52

Fitting 7" bridging will not be the easiest task, cutting them exactly and fitting etc.
So maybe:

Depending on you cash flow, if you can source straight 7 by 2 " you could screw stitch them to the side of the existing, ideally you will need an angle drill.
If you go that route, I would mark out and drill the holes in the new 7 by 2 and have the screws in place before dropping them down for fitting, make the project easier, leaving them far enough up from the bottom edge to allow sideways screwing.
Then add the ply as suggested earlier, screws at 150-200 mm max

kieran.

If its an option I would lift the 2 x 2 batten and I would install 6 x 2s independent of the the old floor joists. Let the old floor joists support the ceiling and the new floor support the floor loads. If the centres on the new floor joists could be decreased all the better. Best to get an engineer to look at it though to give you proper advice.

SC024

take out the existing 2 x 2s, get new lengths of 7 x 2 drop them in beside each existing joist ensure the new ones are sitting on something each end or fixed to wall plates with joist hangers then fit 2 rows of bridgings 1.1 metres in from either end. fill between joists with rockwool to help deaden sound. Screw new 18mm OSB back down ( screws @ 200mm centres & 30mm in from edge of each sheet. ensure sheets are cut so they are halving on each joist. You will most likely end up re-painting ceiling below & probably the skirting / walls of the room upstairs too.

if you use 3.6 metre lengths of 7 x 2 you will have less waste.

Nolic

kieran. wrote: »

If its an option I would lift the 2 x 2 batten and I would install 6 x 2s independent of the the old floor joists. Let the old floor joists support the ceiling and the new floor support the floor loads. If the centres on the new floor joists could be decreased all the better. Best to get an engineer to look at it though to give you proper advice.

What do you mean "If the centres on the new floor joists could be decreased all the better"

Nolic

SC024 wrote: »

take out the existing 2 x 2s, get new lengths of 7 x 2 drop them in beside each existing joist ensure the new ones are sitting on something each end or fixed to wall plates with joist hangers then fit 2 rows of bridgings 1.1 metres in from either end. fill between joists with rockwool to help deaden sound. Screw new 18mm OSB back down ( screws @ 200mm centres & 30mm in from edge of each sheet. ensure sheets are cut so they are halving on each joist. You will most likely end up re-painting ceiling below & probably the skirting / walls of the room upstairs too.

if you use 3.6 metre lengths of 7 x 2 you will have less waste.

What's the best type of bridging?

1. Straps
2. Crossing
3. Solid?

the_pen_turner

Nolic wrote: »

What do you mean "If the centres on the new floor joists could be decreased all the better"

it means add in more timebr and have a smaller gap between them

the_pen_turner

Nolic wrote: »

What's the best type of bridging?

1. Straps
2. Crossing
3. Solid?

herringbone is stronger but a lot more work. it would be better to add in an extra row of solid

kieran.

Nolic wrote: »

What do you mean "If the centres on the new floor joists could be decreased all the better"

We don't know what centres your existing joists are at. If the new joists could go in at 200 or 300mm centres it would be better.

Without actually bolting the new joist to the old it is quite hard to get any true composite strength that why your safer go with new joists remote from the existing ones.

SC024

Nolic wrote: »

What's the best type of bridging?

1. Straps
2. Crossing
3. Solid?

solid

Penn

kieran. wrote: »

We don't know what centres your existing joists are at. If the new joists could go in at 200 or 300mm centres it would be better.

Without actually bolting the new joist to the old it is quite hard to get any true composite strength that why your safer go with new joists remote from the existing ones.

The issue with new joists between existing is the likelihood of existing services between (and possibly through) joists. Much simpler to install solid bridging between the joists and some plywood or OSB sheeting over the joists.

Nolic

Penn wrote: »

The issue with new joists between existing is the likelihood of existing services between (and possibly through) joists. Much simpler to install solid bridging between the joists and some plywood or OSB sheeting over the joists.

The current spacing between joists is 400mm.

Does bridging strengthen the integrity of the floor or just prevent bouncing?

Calahonda52

Penn wrote: »

The issue with new joists between existing is the likelihood of existing services between (and possibly through) joists. Much simpler to install solid bridging between the joists and some plywood or OSB sheeting over the joists.

It depends on the OPs skill set.
It also has the + of levelling the floor

Bridging is always done before the ceiling is put on.
retro-fitting well fitting bridging will inevitably lead to nails being popped in the ceiling below and possibly even cracks.

Penn

Nolic wrote: »

The current spacing between joists is 400mm.

Does bridging strengthen the integrity of the floor or just prevent bouncing?

It doesn't necessarily strengthen the integrity of the floor, as the loading is still taken by the joists, but it creates more structural ties between the joists so it helps spread some of the load to the adjoining joists. It will most reduce (but not totally prevent) bouncing of the joists.