Block and beam v ground bearing floor slabs & GRP roofing

[u587162]

Just had the following comment from the plan sheet / outcome from my private building inspector.

For an area of approx. 60m2 of new extension, how much more will block and beam cost me compared to the alternative and which is better? I understand B&B is quicker to install than the other but are there any other advantages. Would my architect have proposed B&B due to trees near by?

Please provide manufacturers details to justify the adequacy of the proposed block and beam floor construction. Subject to item 2 above and the ground conditions found on site it may be acceptable to provide a ground bearing floor slab as specified for other areas of the work. Advisory - If underfloor heating is proposed in areas where a ground bearing floor slab is to be provided it may be more effective to install the floor insulation above the concrete slab with a slightly thicker screed.


And separately why does the installation of a GRP roof need to be done by a registered installer (another condition he put). Surely not all roof installations need to be registered?


Thanks.

 

[jeds]

I prefer to specify floors that match the existing house - for continuity - and would only specify a beam and block floor if conditions dictated. Ground bearing slab is the cheapest option and removes potential issues with ventilation etc. As for the roof, I know of no regulation that says you have to use a 'registered installer'.

 

[u587162]

The building inspector said that "The reason that the GRP roof has to be installed by a registered is because that is what is specified on the manufacturers BBA Certificate."

How is the floor made up with B&B if I plan to have UFH? Do those celotex/Kingspan go on top and then screed and then UFH?

 

[^woody^]

Any system roof covering needs to be installed in accordance with the manufacturers instructions. Typically that will mean that the manufacturer specifies trained operatives, and the BBA cert will state this.

If there's no BBA cert, and you want to use any old installer, then you'll need to prove that the system will last and is suitable.

The floor supplier should detail the floor detail installation and you just give that to the inspector. It just means installing it lower to allow for the insulation and screed, but some systems have the insulation between and under the beams, and then you use less insulation under the heating pipes.

 

[u587162]

1. I thought GRP is a generic product name. Surely the many roofing felt suppliers suppliers dont required "licenced" or registered roofers?
2. By having a GRP roof, is it highly unlikely my roof will ever leak from the top surface? If it ever does, how long is this usually guaranteed for?
3. Is insulation always going to be required then whether you use B&B or ground floor slabs, does one method use less?

Thanks.

 

[^woody^]

There are several GRP systems. Each may use differing materials and methods, and you don't want one contractor applying system A in the same way he applied system B on his last job.

Felt is felt. It's applied the same way on every job.

The manufacturer will provide a guarantee for its system. But only if installed by its registered and trained contractors. Some systems can be given a top coast at a future time to extend its life. Any system can fail in a few years if not installed properly, or not suitable for the roof/location, or if the roof structure is inadequate.

Insulation is always required for floors, but the type, location and thickness is down to design requirements