plumbing tf new-build with service cavity

Hi

I'm going for a TF build with a 35mm service cavity. I am also opting for radiators as the heating system - and want the piping to come out from the walls (as oppsed to up from the floor) for all rads.

I am just about the pour the floor (next week).

The plumber wants to lay the piping to the rads under the floor at this stage of the build but I would have assumed it would make a great deal more sense to wait until the tf is up and then do the piping in the service cavity area - isn't that the benefit of having a service cavity - or I missing something?

Anyone into plumbing who can offer an opinion as to use of service cavity in this regard?? All thoughts appreciated.

Nowadays most plumbers prefer to drop the flow/returns to radiators from the above heating mains that are running above ceiling level. This is fairly standard with the pipes running in service ducts. As to why your plumber is running them under your concrete floor I don't know. Maybe he has made provisions for this method already. With the advent of modern fully pumped pressurised heating systems it is becoming common practice to install 'drop' systems in timber-frame construction.

Thanks for replying villa - is there any particular advantage in using a drop system as you describe it? Is it just a case of what the plumber is used to? I would have assumed it would be easier to work with pipes etc when the actual timber frame is up rather than working on concrete floor with the aid of plans and measurements, but to be totally honest I know nothing about plumbing and what the best way to plumb a new house is.

The drop system is much faster and easier to install in TF construction and is a very popular method employed by plumbers in housing estetes. The heating sytem will be sealed which will complement the drop system of heating pipes. Your plumber may not be used to installing drop systems and running pipes in service cavities.
An advantage of a drop system is that there will be no pipework buried under your concrete slab should anything go wrong at a later stage
Drop systems are not as efficient if used on an open heating system - utilising a solid fuel heating appliance, stove, range, back boiler etc. If you are fitting one of these appliances along with another heating appliance, oil/gas your plumber would be right to install the pipes under the ground.

Drop systems are probably slower to install these days. Most installers now favour a manifold system I.E every radiator having it's own run of pipe back to an exposed central point (no fittings underfloor or unexposed). So ten rads = 20 seperate pipe runs.

Much easier to run that many pipes on a pre floored base as opposed to drilling countless holes in joists.

Also, if a drop down system is employed, every ground floor radiator will need a drain off cock attached. Many TF homes that were mass produced don't have a manifold system because of installtion cost.

Why not sit down with your installer and question why they want to do what they are doing. Thay work for you, and should be more than happy to explain everything to the last detail.

villa is correct when they state the a pressurised system can be run almost anyway. Unsealed systems have different rules. Explain to your installer how you want it done (it is your home and this is the only time you have to get it right), they should then discuss your options on why it can't be done or "thats a great idea"

Good Luck.

That's interesting Davy. The plumber was talking about having some space in the utility room for a manifold.

So he's obviously going for the system as you describe it. I'm still unclear though as to whether there's any reason (or advantage) in running the pipes under the floor or within the service cavity. If there's no joinings etc, I guess either way is fine as long as the job is done well.

My main reason for asking the question here is that I'm arranging for the groundworks to be completed to floor level next week and just want to get a couple of opinions from other (more knowledgeable) people before I commit to doing things one way or another!

Thanks for your reply.

A couple of comments I'd make, based on my own experience, and that of others I know of.

If you're using copper piping in particular, I'd never put it under a conc floor. A good friend of mine right now, with a 28 yr old house, is suffering from what goes wrong with that: ultimately, the copper reacts with the floor, and leaks. The entire GF is, essentially, destroyed. Secondly, there can be an issue over time with mechanical stresses in the pipe manifesting as leaks, through cracks/joints etc over a long period of time (this is especially true of pressure systems). Now I know you'll say that it should be insulated etc, and you're right, but the fact is, most plumbers are still using 6m lengths of pipe, joined. Want to guess where the joints are ???? Exactly....under the floor......and my experience is that the the quality on-site is what lets the whole thing down. Simplest expedient, for me: no copper allowed. (and forget GB pipe.......)

I would only use a plumbing system where there are no connections whatsoever, under a floor. If this means copper is out, then so be it. Actually, I want to great lengths not to have any copper, in my house, and insisted on Hep2O, instead

OP - dig in - this is your house - if you don't want rising pipes (even for cosmetic reasons), tell him - politely - 'No'.

Whether copper/other, is up to you.

All my experience is with copper and i find it's down to the skill of the installer, If used properly copper is a beautiful thing and long lasting, if not stand back and get the bucket

I'd agree with gary71. It takes a skilled craftsman to install copper pipe properly and there is nothing wrong with either copper or mild steel buried underground if it is supported and insulated properly. Copper and Mild steel pipe will most definitly corrode if there is contact with cement based concrete .the thing to do is to make sure that this will not happen.Most commercial/industrial installations use these pipes all the time.
Polyethylene,Polybutylene pipes take the skill factor out of plumbing making it easy for use by anyone including handymen.
There is nothing wrong with this type of piping material as it is a lot easier to use and joint but it looks gastly when exposed. Above ceiling joists and in behind service voids this type of pipe has a huge advantage over rigid steel or copper pipes. Have a chat with your plumbing contactor and ask him why he wants to run the pipework under the floor. He may bring all the pipework under the floor back to centrally located manifolds and if using flexible polyethylene-Qualpex, Polybutylene-Acorn he should not have any joints under the concrete slab. Be careful with connecting these pipes directly. From my experience during the celtic build madness plumbers or many of their inexperieced apprentices over bent the pipe when connecting to fixtures including radiator valves, leading to the collapse of the pipe and eventual failure. This kink in the pipe is sometimes missed because the plumber covers the pipe that is coming out of the floor with a short section of white plastic electrical trunking pipe

villa 1 said:

I'd agree with gary71. It takes a skilled craftsman to install copper pipe properly and there is nothing wrong with either copper or mild steel buried underground if it is supported and insulated properly. Copper and Mild steel pipe will most definitly corrode if there is contact with cement based concrete .the thing to do is to make sure that this will not happen.Most commercial/industrial installations use these pipes all the time.

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That's as I said - done properly, corrosion won't be a problem, but as you've said, this is all down to the skill of the man on the job. Unfortunatley, attention to detail is not the forte of many....

Polyethylene,Polybutylene pipes take the skill factor out of plumbing making it easy for use by anyone including handymen.

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as you say yourself, in this market, you need all the help you can get !

..... if using flexible polyethylene-Qualpex, Polybutylene-Acorn he should not have any joints under the concrete slab. Be careful with connecting these pipes directly. From my experience during the celtic build madness plumbers or many of their inexperieced apprentices over bent the pipe when connecting to fixtures including radiator valves, leading to the collapse of the pipe and eventual failure. This kink in the pipe is sometimes missed because the plumber covers the pipe that is coming out of the floor with a short section of white plastic electrical trunking pipe

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I don't think any pipe under a floor should have a joint, irrespective of what it's made of. And with copper/steel, you need to be MORE careful than using poly pipes.
As for connecting those pipes directly, the single biggest problem is connecting using the wrong fittings. Why in god's name we don't use proper metric, escapes me. You get people trying to connect TRV's etc, and mixing olives/tape to make the thing work. All because they wouldn't buy the proper fitting in the first place.

Compressed air, hydraulics, fuel, all gave up using compression fittings years ago, yet here we are, with ambient/low pressure systems, using rigid compression fittings - and the 'skill factor' is back again....

Hi Neehallow. Did you pour your floor yet and did you get a chance to talk to your plumber about his installation method?

Hi Villa

Not got to that stage quite yet (delayed by a blocklayer with a newborn baby!) Will be meeting the plumber over the weekend again and he'll be on the job next wed/thur - gonna print out all the replies here and have a scan through them with him when we meet and see what he thinks.

He has a good reputation and has plumbed heaps of local houses over the past decade (and he's pretty much out next door neighbour too - which can't be a bad thing if something goes wrong!)

Will let you all know how I get on - thanks all for the comments - very helpful

No-one 1st fixs houses in copper anymore, far cheaper in plastic pipe.

Commuicate with all the trades and they should be all happy to explain what they are doing and why. You are paying for a service so avail of it. This is the right time to sort things.

Hi all - well, I said to Villa I'd come back with some info when the job was done - so here I am. Basically DavyJ was on the money when it came to how the plumber doing my work has set things up - manifold system, all rads with separate runs, plastic (or polywhatever) pipes, all laid under the ffl so as to avoid going through loads of joists.

All done now and just waiting to pour floor. Looks spot on as far as I can see, all my scribbled (but incredibly accurate!!) measurements have been perfectly adhered to. So far so good & thanks for all the views and opinions.