Should new central heating pipework under floorboards be lagged?

[Schooliform]

Hi, can anyone knowledgeable advise me on this? Having a new central heating system installed in our 1930s detached house. New boiler (combi), new radiators in new positions, all new pipework. Removal of ancient floorstabding boiler & hot water cylinder and ancient radiators. The whole lot, huge job, £12k plus costing us extra to remove the lead pipework. Pipes are mostly laid now but system is not connected yet & pressure not tested yet. Husband enquired about pipe lagging as it hasn't been done yet & Plumber today has said it's not needed as the pipes themselves are insulating (HEP pipes I think they're called). They're running under the floorboards throughout the house. Surely this can't be right and they should all be lagged? Not before the system is tested perhaps but before the job is finished?

Had a Google and I think it forms part of building regulations to lag new pipework.

He's a gas safe plumber we've used before & so have our family members, more than once, so it isn't in his interest to do a bodge job as he gets repeat business from us, but equally this just doesn't seem right. Surely without lagging the pipes could freeze in winter?

Stupidly I have now realised lagging isn't specifically mentioned in the quote but I would have thought this would be a standard part of a new system installation.

Would be grateful for any advice.

So call out building control, now. Then you have your answer with evidence one way or the other. They normally visit within a few days

I would lag them, but I also wouldn't use plastic for heating. That's just me though.

Do you have a picture of the pipes or more details. Google not showing anything for HEP pipes. In theory if they already come insulated then no they won’t need lagging. Are there no details on his quote?

Aside from that when you say under the floorboards do you have an old suspended floor? In that case yes they should be lagged/insulated as this space is essentially open to the outside air via airbricks. But in general interior pipework would not necessarily be lagged if it’s within the interior of the house.

The worry with calling building control is if we damage the relationship with the plumbers what is stopping them from just downing tools and leaving us with an unfinished system. We've paid the majority of the fee already as they wanted a substantial advance deposit which seemed reasonable given the large amount of initial outlay of stuff they had to get from the builders merchant.

I didn't even know a new system would be subject to building regs - it's only though googling we've found out it might be. Happy to be corrected by anyone who knows for sure

The quote doesn't mention lagging at all. I thought it would be a standard part of a new installation. Yes suspended floor with void underneath.

HEP pipes are these: https://www.toolstation.com/hep2o-barrier-pipe-coil-white/p98061

I would have thought they would need to be lagged yes.

We are just about to embark on a replumb of a similar age property and our plumber said he wouldn't touch plastic pipe, he advised copper all the way. Plus we are having all the pipes that run under the ground floor moved so that they run in the space between the upstairs and down - keeping all the heat in the house. Seems madness to have pipes in the floorspace! Our were extremely badly insulated too, so losing loads of heat to the ground or the attic.

Just to add moving the pipes does mean we need to chase in new pipes down the walls in the downstairs instead of up from the floorboards. Of course this adds to the expense!

Yeah that’s just flexible plastic pipe with push fit connections. It isn’t insulated. It’s probably ok to use but should be lagged under the suspended floor. It’s also important that the type of pipe used is the “barrier” type with an oxygen barrier to prevent oxygen entering the system and causing your radiators to rust.

This is one of those situations where ChatGPT (other AI tools are available) can be quite useful. Here’s what it had to say:

In the UK, HEP₂O (plastic) central-heating pipes do not automatically need to be lagged simply because they are HEP₂O. The requirement depends on where the pipes are located, not the pipe material.
Generally:

• Pipes running through unheated spaces (lofts, garages, ventilated floor voids, external walls, etc.) should be insulated to reduce heat loss and help protect against freezing.
• Pipes within the heated part of the house (between heated rooms, within internal walls, under upstairs floors, etc.) are often left unlagged because any heat they lose still contributes to heating the home.
• For new or altered heating systems, building guidance generally expects pipework outside the heated envelope to be insulated, with heat loss from uninsulated pipes only allowed where the heat is “always useful”.

If you’re asking because you’ve had HEP₂O installed and are wondering whether the installer should have lagged it, a useful rule of thumb is: ✅ Lag it if it’s in a loft, garage, under suspended timber floors, or any other cold space. ❌ Usually not necessary if it’s running through heated rooms or floor voids between heated rooms.

Yes, you need sign off. Normally a visit early, half way and on completion of the work.

Gas Safe engineers self certify their work for building regs under the Competetent Person Scheme.

This means that they can install notifiable appliances (such as boilers) without needing independent approval from local authority building control.

https://www.gov.uk/guidance/competent-person-scheme-current-schemes-and-how-schemes-are-authorised

Yes, but if OP is concerned the work is not spec'd properly, or she wants reassurance, that's how to find out.