Fixing water pipe in passive house

[Besidethewye]

Hi there - newbie here and apologies if I am repeating and reviving a discussion that's been done to death.  

 

Just about to start the first fix plumbing in an MBC passive house with the smart ply air tight board on the twin stud walls.  I am impressing on everyone the need to not compromise the airtight layer and wondering what the best approach is going to be with clipping pipes (and cables) on the walls in the service void to avoid holes in the air tight board.  If indeed we need to worry - presumably if we have neatly seated screws in each hole the sealing is pretty effective and screws ups should be redone with holes taped?

 

Any suggestions gratefully received.  

[Jeremy Harris]

Welcome.

 

I fixed all our pipes and cables to the sides of the counter battens to avoid penetrating the VCL board, but in places where this wasn't practical, like fixing electrical backboxes, I used 45mm back boxes and a piece of 6mm plywood glued and screwed to the VCL board (I  used ordinary PU foam glue).  Back box screws were sealed with a tiny drop of the same glue before tightened fully home, as they went through the ply and into the VCL board.  This also had the advantage of spacing the back boxes out so they were around half way through the depth of the plasterboard, which makes it easier for those fitting the plasterboard to cut out (they just put the board in place, tap it where the box is and the edge of the box marks the board).

 

I found using PU expanding glue was a lot easier and quicker than taping over screws, but 90% of our pipes and cables are fixed to the sides of the counter battens anyway.

[Besidethewye]

JS thank you for that - that sounds like belt and braces (and there's a lot to be said for that!).  

 

On that basis you're spreading pipes (and cables) around rather than running them up together.  Without having started I am assuming we will have plenty of places where things have to cross and with 35mm to play with it may all get a bit tight.  

 

I am anticipating a certain amount of resistance to being really fussy about the airtight layer but good to have some back up!

 

[Nickfromwales]

1 hour ago, Besidethewye said:

JS thank you for that - that sounds like belt and braces (and there's a lot to be said for that!).  

 

On that basis you're spreading pipes (and cables) around rather than running them up together.  Without having started I am assuming we will have plenty of places where things have to cross and with 35mm to play with it may all get a bit tight.  

 

I am anticipating a certain amount of resistance to being really fussy about the airtight layer but good to have some back up!

 

"Crossovers" should be done in the ample joust space and then the services dropped in order so they don't have to cross again . Not so important with cables but deffo with pipes. 

You shoukdbt actually have that many pipes in the same single service void so a bit of planning goes a long way ?

[Nickfromwales]

Oh, and welcome to the forum ?

[Jeremy Harris]

As @Nickfromwales says, you shouldn't have too many pipes in the same outside wall service void.  In our build only two H & C  pipe runs came down external walls, and it's easy to run one pipe one side of a counter batten and the other pipe the other side of the same counter batten.  I had to cut slots in a few counter battens to run pipe horizontally in one location, where it made sense to run the pipes down the side of a window, then across to where the pipes came out to feed the kitchen sink, dishwasher and boiling water tap.

 

In the downstairs WC I managed to run the two pipes down either side of a batten to come out right behind the basin, and then ran these pipes on the surface of the plasterboard, behind the fitted units in the WC, through the stud wall to the adjacent utility room, where the pipes run behind the washing machine, then behind the utility room fitted units to the sink.

 

Most of the long pipe runs are on the underside of the floors, rather than the external walls, and with these I took care to take photos and mark where they were on the floor surface above.

[Besidethewye]

Nick and JS thanks again - will indeed aim to have as few pipes against the external walls as we can (things are a bit complicated by the shape of the build and the ring of steels/glulam beams that separate the inner part of the build from the rest at first floor floor level).  But will make sure we have a plan before we go too far with fixing things in place!  

[Nickfromwales]

33 minutes ago, Besidethewye said:

Nick and JS thanks again - will indeed aim to have as few pipes against the external walls as we can (things are a bit complicated by the shape of the build and the ring of steels/glulam beams that separate the inner part of the build from the rest at first floor floor level).  But will make sure we have a plan before we go too far with fixing things in place!  

You can request penetrations in the steels ( prior to installation) and you can make holes in the Glulams. 

For eg on one build I have requested penetrations through 254mm UC's big enough to take a 110mm FW pipe through, and also, in the same steel, a penetration ( letterbox shape ) 51mm x 300mm for pipes and cables. They will be plated to fortify the section where the steel is compromised. 

The 315mm glulam will have 2x 60mm holes mid-span & mid section for 2x 50mm grey waste water pipes. All passed by MBC's SE. 

[volcane]

The interior OSB of my house has been directly battened with 45mm battens at 400 centres, this is a problem for electricians who have priced the job who all want the house counter-battened to allow the required 50mm clearance for cables and to prevent a screw nicking a cable.

 

Is 50mm clearance a definite? is there any way to avoid having to counter batten?

 

thanks

 

[ProDave]

1 hour ago, volcane said:

The interior OSB of my house has been directly battened with 45mm battens at 400 centres, this is a problem for electricians who have priced the job who all want the house counter-battened to allow the required 50mm clearance for cables and to prevent a screw nicking a cable.

 

Is 50mm clearance a definite? is there any way to avoid having to counter batten?

 

thanks

 

They are talking B******S Tell them to go and read the CURRENT regs.

 

There Is no 50mm requirement. It used to be under a previous version of the regs, that if a cable was more than 50mm deep you could avoid the need for RCD protection, that is all. But now everything (just about) has an RCD anyway. Directly behind 9mm plasterboard would be perfectly fine.

 

IMHO 25mm is plenty for a service void where just cables are going. 25mm battens and 12mm plasterboard is just about perfect for 35mm back boxes. I only used a deeper service void in the utility room where more pipes are going.  I even had no trouble dropping the 15mm pipes down to the kitchen sink in the 25mm service void.

[volcane]

Thanks for that, are the regs UK wide? I'm in NI which is often well out of sync.

My current 45 should be enough even when the battens have to be drilled to allow cables.

 

 

[ProDave]

Wiring regs are UK wide. England and Wales add a few extras with Part P of the building regs but we don't have that here in Scotland or NI.

 

Re holes in battens, I pre empt this and when fitting the battens leave a small gap at 450mm above FFL for socket cables and another at 1200 for light switch cables. It saves a lot of drilling later.  I just wish I could get some of the local joiners to be similarly helpful.

[volcane]

19 hours ago, ProDave said:

Wiring regs are UK wide. England and Wales add a few extras with Part P of the building regs but we don't have that here in Scotland or NI.

 

Re holes in battens, I pre empt this and when fitting the battens leave a small gap at 450mm above FFL for socket cables and another at 1200 for light switch cables. It saves a lot of drilling later.  I just wish I could get some of the local joiners to be similarly helpful.

@ProDave I've been trying to find current regs to give to the electrician but can't find the the necessary document. The electrician is worried that unless there was a clear 50, some one is liable to hit a cable when putting up plasterboard.   I've had serious trouble trying to source an electrician and don't want to annoy the one who has shown interest in doing the job.

 

many thanks

 

[Jeremy Harris]

1 hour ago, volcane said:

@ProDave I've been trying to find current regs to give to the electrician but can't find the the necessary document. The electrician is worried that unless there was a clear 50, some one is liable to hit a cable when putting up plasterboard.   I've had serious trouble trying to source an electrician and don't want to annoy the one who has shown interest in doing the job.

 

many thanks

 

 

The electrician is required to have access to a copy of the current regs, in this case BS7671:2017 Amendment 2.  After next January it will have to be to BS7671:2018.

 

It's not optional, in order to trade as an electrician he HAS to be up to date on the applicable regs.

[ProDave]

You can buy the regs for somewhere between £60 and £80, and if buying now of course get the 18th edition. But as stated if the electriaian does not have his own copy, you are talking to the wrong electrician.

 

There is always a risk, no matter where you put a cable, that some other trade might drill through it, which is why you test the circuit before applying power. It does occasionally happen and then you have to find and fix the fault, but not often.