Suspended timber ground floors and rodents

pawdee

Hi all,

I'm about to build an extension with a suspended timber ground floor (joists supported on structural steel pedestals). So I'll have 225 x 40 joists, 150 mm rigid insulation supported by battens fixed to joists, vapour barrier / air tightness membrane (?), tape to joints and plywood on top.

The main thing I'm worried about is how to keep out Mr Rat. Should I include some kind of mesh or cement board? I'll be bringing the cladding right down to the ground all around and allowing for ventilation of the approx 300mm deep space beneath.

Any advice on how to achieve this economically would be greatly appreciated. I'm also open to correction and criticism if my floor build up described above looks wrong.

Thanks in advance.

BryanF

That’s a tough one as the floor structure needs to breathe, What centers are the steels?

I’d be laying breather felt on cold side of insulation and batten cavity for ventilation, stainless steel insect, etc

I’d be considering a breathable insulation layer under the joists also.

Re vermin and the underside finish, selection may be down to centers of the steel? Or whether you’d Be happy to assemble the floor in sections, but then you’ve to worry about install tolerance and closing the junctions.

kevcos

Good article here that was recently posted in a similar thread:
https://www.ecologicalbuildingsystems.com/Ireland/Blog/Post-Detail/A-Best-Practice-Approach-to-Insulating-Suspended-Timber-Floors

pawdee

BryanF wrote: »

That’s a tough one as the floor structure needs to breathe, What centers are the steels?

I’d be laying breather felt on cold side of insulation and batten cavity for ventilation, stainless steel insect, etc

I’d be considering a breathable insulation layer under the joists also.

Re vermin and the underside finish, selection may be down to centers of the steel? Or whether you’d Be happy to assemble the floor in sections, but then you’ve to worry about install tolerance and closing the junctions.

Thanks Bryan, the only steels will be stanchions similar to post supports albeit heavy duty with base plates bolted to concrete pads. The spans are less than 4m so perimeter and intermediate steels aren't required. That's what I'm told anyway but I'll be getting everything signed off by an engineer. I'll be doubling up joists with toothed connectors all around the perimeter.

To summarise, I'm building a reasonably lightweight timber framed extension, clad in slate with a flat roof in a very restricted site (mid terrace town centre). It'll be a shoebox shaped building glazed at one end.

The only excavation and concrete will be for the 8 pads to support the steel posts. That's the plan anyway. All of this will be built and assembled on site because, while the site is restricted from an access point of view, I have a large yard in which to store and assemble all the components.

If you could PM me the type of insulation you recommend that would be great. Would it be supported by a mesh?

Sorry for the long missive and thanks again for your contribution.

pawdee

kevcos wrote: »

Good article here that was recently posted in a similar thread:
https://www.ecologicalbuildingsystems.com/Ireland/Blog/Post-Detail/A-Best-Practice-Approach-to-Insulating-Suspended-Timber-Floors

Thanks Kevcos. Figure 8 looks very like what I'm trying to achieve. I'll just need to incorporate some kind of mesh to keep the furry fellas out.

BryanF

Pawdee
I’d recommend 50mm min wood fibre insulation such as gutex under the joists and cellulose (loose fill)or mineral wool (batts) in between. All breathable materials. Cellouse will help with sound.