Drill joists or box-in ceiling corner?

[Crowbar hero]

I'm trying to figure out the best routes for hot and cold water piping for my extension.  The boiler is high in the middle of the gable wall, and I need to get hot & cold water across a lot of floor joists to each end of the space. Building regs suggest the best place to drill joists is around the 1/3 span location (roughly) - which mean adding several metres to the pipe run to come away from the wall, traverse across the joists and go back to it.

 

I'm tempted to run the pipes below the ceiling line in a boxed off corner where the wall meets the ceiling, but it would mess up an otherwise rather crisp ceiling corner. 

 

Are there any other alternatives I'm missing? 

[Bonner]

Not sure which regulation you are looking at but most builders would just drill the joists where needed. You should avoid the middle third of the span where bending stress is highest and always drill mid-depth (neutral axis). What size joists and pipes?

[Crowbar hero]

1 hour ago, Bonner said:

Not sure which regulation you are looking at but most builders would just drill the joists where needed. You should avoid the middle third of the span where bending stress is highest and always drill mid-depth (neutral axis). What size joists and pipes?

joists are 220x47mm - span is 4m

Pipes are most likely 22mm, maybe one or two bigger.

 

I'm following the guidance here:

 

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-4-timber-and-concrete-upper-floors/6-4-18-notching-and-drilling/

 

which seems to be echoed in many other places.

 

Edited August 25, 2022 by Crowbar hero
corrected units, better link

[Miek]

Boxing in seems like more work than drilling to me. Use flexible plastic pipe and an oversize hole and it's easy enough. 

[Temp]

On 25/08/2022 at 12:39, Crowbar hero said:

Are there any other alternatives I'm missing? 

 

If you are considering drilling the joists then presumably its not been plasterboarded yet? 

 

Could you fit counter battens at 90 degrees to the joists to form a void below them to run the pipes in? The battens would need to be the same depth as the diameter of the insulated pipe. The ceiling would be the same amount lower.  

 

[Mr Punter]

NHBC recommend avoiding the middle 20% of the span, so if you are drilling you only need to go a bit one way or the other if you are dead centre.  Max hole size for your joists is 55mm.

[joe90]

For reference https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists. (I hate boxing in, looks naff IMO).

Edited August 26, 2022 by joe90

[Crowbar hero]

1 hour ago, Temp said:

 

If you are considering drilling the joists then presumably its not been plasterboarded yet? 

 

Could you fit counter battens at 90 degrees to the joists to form a void below them to run the pipes in? The battens would need to be the same depth as the diameter of the insulated pipe. The ceiling would be the same amount lower.  

 

Yep, the extension is barely more than a shell with no internal finishes at the moment.

I'd rather not lose any ceiling height If I can help it, but it's an idea.

 

[Nickfromwales]

Structural engineers can help you decide where to drill that number of holes. You should be fine, don’t go to the expense and ugliness of boxing in etc 👎.

You can stop the insulation ( if it’s actually required ) either side of the joist to make the holes smaller. 
What is the 22mm feeding? Not hot water? 

[Nickfromwales]

FWIW, I’m on a TF house atm, with 300mm glulams and I got permission for pre determined / agreed location etc 96mm holes. Can be up to a 1/3 of the depth dependant on thickness of wood. 

[Crowbar hero]

Hi Nick,

 

The 22mm is for CH flow and return, and also hot & cold water - I want the pipes as larger as practical to reduce flow speed and thus noise.

[Crowbar hero]

1 minute ago, Nickfromwales said:

FWIW, I’m on a TF house atm, with 300mm glulams and I got permission for pre determined / agreed location etc 96mm holes. Can be up to a 1/3 of the depth dependant on thickness of wood. 

 

Glulams are a different kettle of fish entirely, impressively engineered, but not a lot of space for bodging thing..

[Nickfromwales]

1 hour ago, Crowbar hero said:

Hi Nick,

 

The 22mm is for CH flow and return, and also hot & cold water - I want the pipes as larger as practical to reduce flow speed and thus noise.

You do not want to upsize the hot water pipe. You’ll massively increase the delay in getting hot water out of basin / sink taps. 👎

[Crowbar hero]

33 minutes ago, Nickfromwales said:

You do not want to upsize the hot water pipe. You’ll massively increase the delay in getting hot water out of basin / sink taps. 👎

Good point.. 
I think the bath is supposed to be on a 22mm supply, but rest I can downsize.

[joe90]

47 minutes ago, Crowbar hero said:

think the bath is supposed to be on a 22mm supply,

Why?, my bath, kitchen tap  and showers are all on 15mm with basins and toilets on 10mm, very adequate and quick to get hot water, 22mm is old standard (IMO).

[Mr Punter]

1 minute ago, joe90 said:

Why?, my bath, kitchen tap  and showers are all on 15mm with basins and toilets on 10mm, very adequate and quick to get hot water, 22mm is old standard (IMO).

 

I think the large pipes are a hangback from the gravity systems with a tank in the loft.

[Nickfromwales]

19 hours ago, Mr Punter said:

 

I think the large pipes are a hangback from the gravity systems with a tank in the loft.

Yup. With today’s water bylaws, most taps / other outlets are flow governed by manufacture, so a 22mm feed is pointless.

 

Also, unless this is a monster heat store combi, the cold inlet will be 15mm, so another reason to not employ 22mm hot pipework   

[Crowbar hero]

6 hours ago, Nickfromwales said:

Yup. With today’s water bylaws, most taps / other outlets are flow governed by manufacture, so a 22mm feed is pointless.

 

Also, unless this is a monster heat store combi, the cold inlet will be 15mm, so another reason to not employ 22mm hot pipework   

 

I was considering 22mm for cold water to reduce flow noise - it's pretty terrible at the moment, and all on 15mm, so I figure bigger bore = slower water speed = less cavitation = less noise.

Obviously combined with large radius bends where possible and decent de-burred joints.