DIY Doctor

GifaFloor FHB18 Joins without Joists and no Edge Support

Postby » Mon Dec 30, 2019 12:08 pm

We have a 4x3 bedroom with the following 12 spans:
190, 368, 380, 365, 380, 370, 385, 370, 395, 385, 370, 300

The UFH was installed by builders ready for the GifaFloor FHB18 (18mm). FHB18 is rated at 2kn point load when installed to manufacturers instructions, they estimate to reduce that by 50% that, if joins aren't supported by joists. I have the following two questions:

1) The centres are not 400. Which means joins do not line up on joists, so I drop below the 2kn point load: My architect advised me it is not worth pulling up all the UFH to sister joists, which would probably make it impossible to lay spread plates anyway (squeezed too much). He said as this a bedroom with a small(ish) floor area and centres which are all smaller than 400 I will "probably" be ok; because the manufacturers build in a large degree of safety. I've read first floors should be 1.4kn... So if we are potentially half 2kn (1kn) that has left me a little concerned. Anyone had similar experiences and it has been ok?

2) No edge support on one wall: Architect said that holed 35mm x 35mm x 1.5mm to 2mm steel angle iron will work for edge support. Vertically screw at 200mm centres and pink grip to stop squeezing. This sound ok, and anyone got links to good products they'd recommend? I've seen this, Punched Steel Equal Angle Profile - 1m x 35.5 x 35.5mm 1.5mm. I'm trying to find something a little thicker and longer. Unfortunately my builders need it ASAP, so cannot order from fabricator (such as - Home Page - Daver Steels Ltd)
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DIY asbestos test kits

Postby » Thu Jan 02, 2020 1:42 pm

I have an update with a useful document, which may help other customers in the future. This link is a detailed document on stress load testing and results for FHB 18 and FHB 32: ... 889433.pdf

It also matches what I've read else where. The point load capacity is for a maximum of 3mm deflection, to ensure the boards can be tiled on safely, and not the point at which they break. It seems the point of breaking will have a safety factor and be much higher. I suspect for a carpeted bedroom, with no through traffic I really shouldn't worry about it.

The document shows the perimeter edges are actually slightly weaker than the T&G side joins, and that the loads go up to 6.9kn without breaking, well beyond the 2kn recommended capacity. So I'm feeling more confident now.

For joins without support, does anyone know where GifaFloor rule for a reduction in load capacity of 50% comes from, how it was determined? Why they have that rule for FHB25 and above, and no data for this on FHB18?

Also my searching finds that with chipboard T&G the main issues of unsupported end joins is sagging and creaking. In people's experience with this or similar products, does fibrous boards have similar or different issues, or does the fact they are stiffer make it less of a problem?
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