Studwork - what size timber?

[Johnnyvee]

Hello,
Newbie here so please take it easy on me and can't see that this question has been asked before - apologies if it has.

We have a square "archway" between the dining room and front room that is in a load bearing wall with an RSJ and made out of block work which has been dotted and dabbed onto and skimmed over. I'm going to block it up with studwork and then plasterboard over to have it skimmed. The floors are concrete so the blocks sit on a membrane.
The thickness that I need to make this bit of wall is 160mm though there is a little bit of variance where its a couple of mm out - the square hole that I need to fill in is 2070x1700.
So - I know I need to use pressure treated wood for the footing and sit it on damp proof membrane and fix to concrete floor beneath. Question is - what size width do I buy? 160mm less, say 3mm skim either side gives me 154 left, less 2x12.5mm plasterboards leaves me with 129mm.

Everywhere I look on line no one does timber this size or within a few mm of it. So, do I go for a width above and plane down or do I get say two smaller width pieces and lay them side by side, possibly with a gap between them? This is not load bearing and I will be fitting sound insulation and using 400 centres for strength. Same question for the rest of the studwork really? And apologies if it seems a bit dumb.

Thanks for any advice...

 

[noseall]

Hello,
Newbie here so please take it easy on me and can't see that this question has been asked before - apologies if it has.

We have a square "archway" between the dining room and front room that is in a load bearing wall with an RSJ and made out of block work which has been dotted and dabbed onto and skimmed over. I'm going to block it up with studwork and then plasterboard over to have it skimmed. The floors are concrete so the blocks sit on a membrane.
The thickness that I need to make this bit of wall is 160mm though there is a little bit of variance where its a couple of mm out - the square hole that I need to fill in is 2070x1700.
So - I know I need to use pressure treated wood for the footing and sit it on damp proof membrane and fix to concrete floor beneath. Question is - what size width do I buy? 160mm less, say 3mm skim either side gives me 154 left, less 2x12.5mm plasterboards leaves me with 129mm.

Everywhere I look on line no one does timber this size or within a few mm of it. So, do I go for a width above and plane down or do I get say two smaller width pieces and lay them side by side, possibly with a gap between them? This is not load bearing and I will be fitting sound insulation and using 400 centres for strength. Same question for the rest of the studwork really? And apologies if it seems a bit dumb.

Thanks for any advice...

160mm?
Block it up with masonry + dot and dabbed and skimmed plasterboard = 160mm.

 

[martygturner]

Its just an infill, you could just use 2x4, frame it and batten it out take up any diffrence with plastic packers, there is no need to use pressure treated on an internal wall.

Its up to you if you pack out both sides - which I would advise, ie build your stud down the centre line, you can always use two layers of plaster board, it comes in two thickness, 9.5 and 12.5mm

 

[Deluks]

Agree with Nose, 100mm blocks will see it filled in no time, if you are inexperienced then use ready mixed mortar.

If you are set on timber then you could find a woodyard with a table saw and get them to rip a 6x2 down to size, or do two walls out of 2x2, with a few flat metal brackets joining the two halves together.

 

[endecotp]

If soundproofing is important, building two stud frames from thinner timber with a gap between will be better. Offset the intermediate studs and run the insulation batts unbroken.