Posijoist ducting and runs, how.

[epsilonGreedy]

Is the UK company behind Posijoist guilty of not providing thought leadership on techniques for fixing pipe and cable runs through their open metal web joists? Looking at images online installers are left to wing it, one image shows a copper pipe resting on the lower beam wood section, surly a recipe for creaking pipes as the wood dries. And what about mains cabling, can this ever touch the metal webs?

[PeterW]

The installation guides show how you should do it - cables can be clipped to the webs, they have rounded edges.

 

 

[RandAbuild]

Here's a pic of some of our service runs in pozijoists. The main cable routes were contained in baskets secured along the length of the joist - very neat solution

[Russell griffiths]

I think it is easy to find a pic of a poor installation of anything,

standard practice would be that any pipes should be clipped where they come into contact with an object and as peter said the metal webs have nicely rounded edges to protect cables when they are being yanked about. 

 

More concering are the steel fixing plates on roof trusses, now these are blooming sharp. 

[PeterW]

3 minutes ago, Russell griffiths said:

More concering are the steel fixing plates on roof trusses, now these are blooming sharp. 

 

I have a 1" scar in my scalp from the edge of one of these from 8 years ago !!

[Jeremy Harris]

11 hours ago, epsilonGreedy said:

Is the UK company behind Posijoist guilty of not providing thought leadership on techniques for fixing pipe and cable runs through their open metal web joists? Looking at images online installers are left to wing it, one image shows a copper pipe resting on the lower beam wood section, surly a recipe for creaking pipes as the wood dries. And what about mains cabling, can this ever touch the metal webs?

 

As I understand it, Posijoist licence the construction method to several companies, so it may well come down to who you buy them from as to what guidance you get.  Some manufacturers do publish some pretty comprehensive guidance on fixing them, but I think most people just use their own ingenuity when it comes to how to secure stuff. 

 

Pipes and wiring are easy, as they both have their own fixing rules in their own regulations or general trade knowledge that govern things like fixing types and spacings, it's really just ventilation ducts  where you have to make up your own methods of fixing.  I used a combination of perforated steel strapping and lots of big cable ties when I installed ours.

[epsilonGreedy]

11 hours ago, PeterW said:

The installation guides show how you should do it - cables can be clipped to the webs, they have rounded edges.

 

 

I have read through the three downloadable docs from the mitek.co.uk site, 80+ pages in total with some repetition. Only one page addresses ducting specifically just maximum sizes for conduits, which is the technique most self builders seem to ignore.

 

Google searches lead to images suspiciously lightly loaded with plumbing and electrics. The image posted to this thread is the only one showing a convincing fully loaded Posijoist floor void. I am beginning to think that Posijoists are likely to slow down a professional house build because follow-on trades will need to invent custom solutions for supporting pipes and cables.

[Jeremy Harris]

Just now, epsilonGreedy said:

 

I have read through the three downloadable docs from the mitek.co.uk site, 80+ pages in total with some repetition. Only one page addresses ducting specifically just maximum sizes for conduits, which is the technique most self builders seem to ignore.

 

Google searches lead to images suspiciously lightly loaded with plumbing and electrics. The image posted to this thread is the only one showing a convincing fully loaded Posijoist floor void. I am beginning to think that Posijoists are likely to slow down a professional house build because follow-on trades will need to invent custom solutions for supporting pipes and cables.

 

Bear in mind that there are rules defined in other regulations for supporting wiring and pipework, so my guess is that joist manufacturers don't see any need to repeat these in their advice.

[epsilonGreedy]

1 hour ago, JSHarris said:

As I understand it, Posijoist licence the construction method to several companies, so it may well come down to who you buy them from as to what guidance you get.

 

 

The Mitek documents include an impressive amount of detail for the joist installation stage including awkward edge case scenarios. What is odd is that their no.1 or no.2 selling point is simplicity of installing services and yet the more I think about it I-beams and solid wooden joists have proven solutions that require zero think time or fiddly creativity.

 

1 hour ago, JSHarris said:

Pipes and wiring are easy, as they both have their own fixing rules in their own regulations or general trade knowledge that govern things like fixing types and spacings

 

 

Precisely, you prove my point. The standard way to run a central heating pipe across joists is a top notch and a bit of felt, the very thing that is expressly forbidden with Posi joists. The Mitek official site shows copper pipes resting on the lower timber chord which seems like a recipe for pipe rattles when a person stomps across a bedroom floor, the alternative shown in this thread is a horizontal support with a notch for pipework but am I looking at a notch taken out of the strong back?

 

1 hour ago, JSHarris said:

I used a combination of perforated steel strapping and lots of big cable ties when I installed ours.

 

 

This sounds interesting, if I review your build blog will I find an image of this technique?

 

Anyhow this is the type of technique that Mitek should be providing a definitive example of.  My first thought was to strap a 4" plastic pipe across the joists anchored to the metal webs but then I was concerned this might create an thermally insulated chamber that would cook wiring if it heats up under load.

[Jeremy Harris]

1 minute ago, epsilonGreedy said:

Precisely, you prove my point. The standard way to run a central heating pipe across joists is a top notch and a bit of felt, the very thing that is expressly forbidden with Posi joists. The Mitek official site shows copper pipes resting on the lower timber chord which seems like a recipe for pipe rattles when a person stomps across a bedroom floor, the alternative shown in this thread is a horizontal support with a notch for pipework but am I looking at a notch taken out of the strong back?

 

I fitted standard pipe clips at the right spacing to support the pipes under the top member, or fixed them under the floor on spaced off pipe clips (to help avoid pipes being accidentally hit by screws or nails coming through from above.

 

 

1 minute ago, epsilonGreedy said:

This sounds interesting, if I review your build blog will I find an image of this technique?

 

Anyhow this is the type of technique that Mitek should be providing a definitive example of.  My first thought was to strap a 4" plastic pipe across the joists anchored to the metal webs but then I was concerned this might create an thermally insulated chamber that would cook wiring if it heats up under load.

 

I've just checked my photos, and can't find any really clear ones that show this, as I fitted the acoustic insulation in pretty much at the same time as the ducts, so that hides the fixes, I'm afraid.

[epsilonGreedy]

27 minutes ago, JSHarris said:

 

Bear in mind that there are rules defined in other regulations for supporting wiring and pipework, so my guess is that joist manufacturers don't see any need to repeat these in their advice.

 

 

Their principal rivals who promote I-beams take the opposite approach with ready made conduit knockout panels. The market rewards manufacturers who provide a prescriptive highspeed solution to a problem e.g. Wago boxes.

[PeterW]

41 minutes ago, epsilonGreedy said:

 

I am beginning to think that Posijoists are likely to slow down a professional house build because follow-on trades will need to invent custom solutions for supporting pipes and cables.

 

Quite the contrary !!

 

Standard detail for wiring follows the 17th Edition Site guide  - it doesn't care if you use any type of joist, it specifies the requirements for the wiring.

 

We did a full first fix wiring on a 3 bed 165sqm house in 3 days with PosiJoists.

First fix plumbing took 3 days - 2 days for the new side, and 1 day as there is part conversion and we had to route through and around existing solid 8x2 joists.

MVHR took half a day to run the ducts - no drilling required,

 

I would hazard a guess that using I-Beams we would have added 35-50% to this, and solids would add 100% to this. 

 

Mitek, Wolf and other posi systems are used in pretty much every volume house builder estate now - its the norm not the exception

[PeterW]

23 minutes ago, epsilonGreedy said:

The standard way to run a central heating pipe across joists is a top notch and a bit of felt

 

That is very 1960's copper and traditional build spec...

 

The current way is through or along the joists using Hep2O or similar, transition to copper if needed for aesthetics. Most plumbers also go 50mm down these days so you can't hit the pipe with a screw or nail.

[epsilonGreedy]

@RandAbuild - your photo is very helpful particularly the basket idea for cradling the electric cables.

 

Did you find you needed to think ahead and load up the joist void with extra timber to be used later for service supports? I note the larger diameter black pipe running through the wood support, was that wooden support too large to thread into place after the joists were fixed in position?

[jamiehamy]

 

13 hours ago, epsilonGreedy said:

Is the UK company behind Posijoist guilty of not providing thought leadership on techniques for fixing pipe and cable runs through their open metal web joists? Looking at images online installers are left to wing it, one image shows a copper pipe resting on the lower beam wood section, surly a recipe for creaking pipes as the wood dries. And what about mains cabling, can this ever touch the metal webs?

in short - no. As discussed, and we did on our build, pipe clips for pipes, cable ties for MHRV and Q crimps for cables. Dead easy,really quick and as @PeterW said, massive saving during first fix. 

[PeterW]

11 minutes ago, epsilonGreedy said:

@RandAbuild - your photo is very helpful particularly the basket idea for cradling the electric cables.

 

Did you find you needed to think ahead and load up the joist void with extra timber to be used later for service supports? I note the larger diameter black pipe running through the wood support, was that wooden support too large to thread into place after the joists were fixed in position?

 

Soil pipes need to run parallel to any joist unless you add it when building the floor otherwise you have to leave the end off the building....

[epsilonGreedy]

13 minutes ago, PeterW said:

Quite the contrary !!

 

Standard detail for wiring follows the 17th Edition Site guide  - it doesn't care if you use any type of joist, it specifies the requirements for the wiring.

 

 

Ok but I am not sure why this thread keeps veering towards trade standards. When running your mains cabling through the posi joist void did you implement a metal tray support plinth as described by @jsharris or did you invent a cradle system as shown in the first photo in this thread?

[jamiehamy]

I'm not sure what you're point is? You asked a question about 'thought leadership', and the answer is no - there are standards already in place to route these services - hence why ''veering' towards trade standards. But that doesn't mean they are the only methods, as long as they are not dangerous or contrary to guidance. What method are you planning using?

[PeterW]

1 minute ago, epsilonGreedy said:

 

Ok but I am not sure why this thread keeps veering towards trade standards. When running your mains cabling through the posi joist void did you implement a metal tray support plinth as described by @jsharris or did you invent a cradle system as shown in the first photo in this thread?

 

None of the above...!

 

Sparks used either cable clips on the sides of the posijoists, or where a bundle of cable was created then there is a standard plastic coated strap used to keep them tidy - all standard detail as per the site guide which is the requirement of the Wiring Regulations. That is what you have to follow - not a joist manufacturers installation guide as they are not the expert in this case

 

 

[epsilonGreedy]

40 minutes ago, PeterW said:

That is very 1960's copper and traditional build spec...

 

The current way is through or along the joists using Hep2O or similar, transition to copper if needed for aesthetics. Most plumbers also go 50mm down these days so you can't hit the pipe with a screw or nail.

 

I know this is not true even though I am a rookie.

 

My year 2000 Bryant Homes house used the copper & upper joist notch technique. And earlier this week a young chap (33) was standing in my kitchen listening to my self build plans, after a short career in general plumbing he moved onto a well paid new career path in central heating servicing. His no.1 piece of advice was "whatever you do, do not use plastic piping, the rubber seals always fail eventually".

 

Edit: I now recall he was talking about the quick fit jointing system associated with plastic piping.

 

p.s. I do appreciate your advice. Two weeks ago you shaved £1000's off my self build project with a single sentence observation on my central heating design.

Edited March 1, 2018 by epsilonGreedy
Correction.

[PeterW]

3 minutes ago, epsilonGreedy said:

His no.1 piece of advice was "whatever you do, do not use plastic piping, the rubber seals always fail eventually".

 

He probably needs to speak to Wavin about this.... Hep2O provides a 50 year guarantee - no single copper fitting is guaranteed past 30 years, with Tectite being guaranteed for that ... which ironically has nitrile seals in the fittings....

 

 

[epsilonGreedy]

7 minutes ago, jamiehamy said:

I'm not sure what you're point is? You asked a question about 'thought leadership', and the answer is no - there are standards already in place to route these services - hence why ''veering' towards trade standards. But that doesn't mean they are the only methods, as long as they are not dangerous or contrary to guidance. What method are you planning using?

 

 

If it is so obvious that trade standards provide the answer to my question why have three people offered different fixing solutions in this thread to the same build challenge?

[epsilonGreedy]

7 minutes ago, PeterW said:

He probably needs to speak to Wavin about this.... Hep2O provides a 50 year guarantee - no single copper fitting is guaranteed past 30 years, with Tectite being guaranteed for that ... which ironically has nitrile seals in the fittings....

 

 

See my edit above, I think it was the connections he was referring to and not the pipe material.

[PeterW]

OK

 

The Wiring Regulations require that wiring is clipped or supported at minimum x-mm intervals and other such things which @ProDave or @Onoff can probably quote in their sleep. How you achieve that is entirely up to you (or your electrician) as long as it meets or exceeds the requirements.

 

DHW and Heating circuits don't need to meet as stringent guidelines although the Domestic Services Handbook would advise good practice.

 

 

[epsilonGreedy]

9 minutes ago, PeterW said:

How you achieve that is entirely up to you (or your electrician)

 

 

This is the problem. On most other points of build technique there is a load of advice in books and online or established technique.

 

Such advice is missing when it comes to running stuff through posijoists. It seems that every self builder first sticks their head into the posijoist void and thinks, "woohoo loads of space" and then a little later thinks "hmm, how should I attach things... this is going to be a tad more tricky than I anticipated".

 

I am trying to plan my self build way ahead. I have 6 months to work up a solution so I might start eating 5 Fray Bentos meat pies a week which should create enough material to fashion up a posi joist cable conduit.