18 or 22mm floor boards.

[MikeSharp01]

Time to order the first floor floorboards. 18mm is structurally enough on 400mm centres of our I-joists but I was wondering what the advantage of 22mm might be if it isnt structural. 

[Onoff]

I've one room done in 22mm, 400 centres and affixed with Spax screws. 4 other rooms in 18mm at 400 ctrs and affixed with angular rings. Not a peep from the 22mm room. Feels like a solid floor tbh. 

[MortarThePoint]

I had to replace some old 20mm chipboard and did it with 18mm on shims. Whenever I bounded down the stairs on to that floor I convinced myself I'd go though it some day. I suspect good timber floorboards would be stiffer and inspire more confidence though.

[nod]

I used 22 on i joists Loads of glue on the joists and edges of each board Then 60 mil ring nails fix with a gun 

[joe90]

I used 22mm on i joists at 400mm centres with glue only (I did screw the first row simply so I could push the rest against them). Very firm floor indeed.

[PeterW]

22mm without a shadow of a doubt. Glued to the joists and either screwed or nailed first board and then glue every joint. 5mm expansion joint all round and then use a decent sealant to fill that. 

[nod]

12 minutes ago, joe90 said:

I used 22mm on i joists at 400mm centres with glue only (I did screw the first row simply so I could push the rest against them). Very firm floor indeed.

Try taking a board out that has been glued Solid job 

I used 3x1 under the joists to board onto and prevent any squeaks 

 

[joe90]

My only regret is not double boarding the ceilings or/and using sound resilient bars. Even with sound insulation between I joists sound travels more than I would like between floors.

[Temp]

2 hours ago, PeterW said:

22mm without a shadow of a doubt. Glued to the joists and either screwed or nailed first board and then glue every joint. 5mm expansion joint all round and then use a decent sealant to fill that. 

 

And brush the glue on. Running the bottle along can be too hit and miss.

[nod]

6 hours ago, Temp said:

 

And brush the glue on. Running the bottle along can be too hit and miss.

10 mill gap 

Don’t fill the gap BC are pretty keen on that If it’s not clear all the floor noise will transfer to the walls 

[ToughButterCup]

31 minutes ago, nod said:

10 mill gap 

Don’t fill the gap BC are pretty keen on that If it’s not clear all the floor noise will transfer to the walls 

But you do put that sound insulation stuff in that 10 mm gap ? - sorry can't remember the trade name : what isit?

[Onoff]

14 minutes ago, AnonymousBosch said:

But you do put that sound insulation stuff in that 10 mm gap ? - sorry can't remember the trade name : what isit?

 

AC50?

[nod]

48 minutes ago, AnonymousBosch said:

But you do put that sound insulation stuff in that 10 mm gap ? - sorry can't remember the trade name : what isit?

No nothing 

Leave the gap totally open 

10 mil should be a minimum I used an off cut of floor board as a packer 22mil 

Often on-site we screw packers to the floor to stop the D&D falling through

The ceiling below should be airtightness and the D&B above should also be airtight 

So sealing the edge would have no benefit 

[jfb]

2 hours ago, nod said:

10 mill gap 

Don’t fill the gap BC are pretty keen on that If it’s not clear all the floor noise will transfer to the walls 

Is this the expansion gap you are talking about? (As in rather than the 5mm suggested earlier in thread). Presumably it is dependent on the overall size of flooring?

[nod]

30 minutes ago, jfb said:

Is this the expansion gap you are talking about? (As in rather than the 5mm suggested earlier in thread). Presumably it is dependent on the overall size of flooring?

The floor size does make any difference 

Even the mass produced house builders are keen to make sure a continuous gap is there prior to pre plaster 

Usually someone going round clearing mortar out of the gap 

On TF party walls the gaps are usually 40 mil Plank and boards on spats to save them getting trapped 

 

[MikeGrahamT21]

22mm chipboard everytime for solidness, or if floor height is an issue like it was for me, 18mm OSB3, which will give the same effect.

[dpmiller]

go a couple of inches of poured screed over the chipboard.

[ToughButterCup]

23 hours ago, nod said:

...

So sealing the edge would have no benefit 

I am sure I have heard that acoustic sealant would help. I will dig around and find the reference... 

[PeterW]

I’m pretty sure the robust detail for Party walls ensures that the joists run parallel to the walls and it perpendicular as you would get sound transfer into the blockwork from the joists in any instance. 
 

I’m not convinced by the expansion gap theory either given the material we are talking about (wood / chipboard) has such an incredibly low coefficient of expansion that you could get away with a 1-2mm gap in any event. 
 

For airtightness we seal the skirtings to the walls and floors too so this is a further block to the transfer of sound (which is usually via gaps rather than resonance.)

[nod]

It’s immaterial weather we think we should leave a gap or not or fill it over leave BC will pick up lack of a continuous gap 

 

When we sound coat mainly housing association properties We have to do careful not to bridge this gap 

If you are worried about airtightness seal the floor to the skirting But where is the air going to go ? All should ha already been sealed between the floor and ceiling 

[Mr Punter]

30 minutes ago, PeterW said:

I’m pretty sure the robust detail for Party walls ensures that the joists run parallel to the walls and it perpendicular as you would get sound transfer into the blockwork from the joists in any instance. 

 

You can run the joists either way and either build in or use hangers.

[PeterW]

17 minutes ago, nod said:

It’s immaterial weather we think we should leave a gap or not or fill it over leave BC will pick up lack of a continuous gap 

 

When we sound coat mainly housing association properties We have to do careful not to bridge this gap 

If you are worried about airtightness seal the floor to the skirting But where is the air going to go ? All should ha already been sealed between the floor and ceiling 

So air is normally lost around poorly sealed joist ends into walls and cavities, but I’m struggling to work out which bit of the Building Regs is the issue when it comes to a continuous gap..? I know there are manufacturers installation guides about installing flooring but can’t find anything in the Regs. 

[ProDave]

BC and NHBC inspectors both told me to leave a 3mm expansion gap all the way round between the floor and the wall.

 

IF you need to seal from the floor to the wall for air tightness, your air tight tape can bridge that 3mm gap without stopping it being an expansion gap and I doubt the tape would transmit much sound.  But I can't work out why or where you would be relying on the floor as your air tight layer?  All ours was sealed with air tight membrane before the service void, walls and floor went on.  

 

I did seal the downstairs floor to the wall in the utility room with tanking tape bridging the expansion gap, but that was to stop any water in the event of a washing machine leak getting under the floor into the insulation.  There was already the air tight membrane under the floor.

[Temp]

Google found NHBC..

 

http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2006/Part6/section4/sitework.htm

 

Section 6.4

Expansion gaps should be not less than 10mm wide where boards abut a rigid upstand. For larger areas of boarded floor a wider gap may be needed at upstands and intermediate expansion gaps equal to 2mm per linear metre of floor provided.

 

Edited January 4, 2020 by Temp

[PeterW]

24 minutes ago, ProDave said:

BC and NHBC inspectors both told me to leave a 3mm expansion gap all the way round between the floor and the wall.

 

IF you need to seal from the floor to the wall for air tightness, your air tight tape can bridge that 3mm gap without stopping it being an expansion gap and I doubt the tape would transmit much sound.  But I can't work out why or where you would be relying on the floor as your air tight layer?  All ours was sealed with air tight membrane before the service void, walls and floor went on.  

 

I did seal the downstairs floor to the wall in the utility room with tanking tape bridging the expansion gap, but that was to stop any water in the event of a washing machine leak getting under the floor into the insulation.  There was already the air tight membrane under the floor.

This is fine for TF but traditional blockwork doesn’t have the membranes.