Rasing Joist for Loft Insulation

[Tusses]

it wasn't cheap though, the attic floor is solid as a rock now though.

:?

probably more solid than the ground and 1st floor that gets used every day

:?

builing controll :shock:

 

[kevinr]

An alternative I read about somewhere was to fill the existing void using the material of your choice (usually existing fibreglass) and then use rigid insulation laid at 90 degrees. The boarding then floats on top of the rigid insulation. Apparently the rigid stuff is strong enough to transfer the load to the joists without needing additional joists. This would not be enough if you intended to use the space as a room rather than a loft ofcourse.

 

[MikeG.]

Big Soft Moose (!),

why would you insulate at both rafter level and joist level?

You should have airflow over the outside of the insulation in the loft, whether it be from eaves ventilators or breathable sarking. Airflow within the loft would mean that the rafter-level insulation was surrounded on both sides by cold air..........ie pointless! Airflow only above the rafters would mean a large unventilated void ......potentially dangerous to human health and building structure.

Be careful!

Mike

 

[wizer]

I have been thinking about this lately. I find insulation confusing (I find life confusing, but that's a different matter )

My loft is already boarded and full of storage. The house is 1930's semi with trad felt/tile roof.

Can I do as Tusses mentioned and insulate between the 4" rafters with rigid insulation, then plasterboard or hardboard. OR do I have to leave an air gap? If so which side of the insulation? The felt side I presume?

 

[johnf]

Hi John,

don't ever let Building Control insist!!! Their job is to check compliance with the Building regulations......not to stipulate how you comply. If you can get calculations to show that doing it in chocolate ice-cream is strong enough, then that is good enough for them. Furthermore, a suggestion from Building Control in one circumstance can often be interpreted by Builders as a requirement in all circumstances......as a result, there are lots of myths out there!

I can certainly think of situations where it would be structurally advantageous to build up along the joists rather than across them.......second best in insulation terms, but in some circumstances it may be stronger. Every case should really be assessed on its merits, but in general terms, across the joists is best.

Mike

Hi Mike the main reason the joists go across the joists is so that the insulation works properly

 

[MikeG.]

Absolutely, John........see my earlier posts, where I said just that.

..........but my point here was to say that Building Regs (and their enforcers, the BCO's), aren't as prescriptive as people think. To be really pedantic, the Regulations are extremely loosely written (generally being only one sentence long, or maybe a paragraph), and it is the Approved Documents which show one way of meeting the requirements. If you can show compliance using methods or materials not in the Approved Documents you are still complying with building regs. Most people think the Approved Documents are the Building Regs.

My other point was to make it clear that you can't and shouldn't give broad generalisations (particularly as an Architect), without wrapping it up in caveats.......for instance, the bottom chord of a gang-nail trussed roof may not have been designed to take any load at all, in which case a different approach would be needed.

To sum up.....generally, the top layer of insulation should ususally be at right angles to the lower. However, this won't be applicable in all circumstances. If in doubt, ask!

Mike

 

[AndyG]

Thanks all for your replies. I've got a clearer idea now of the way ahead. I'll get back to the forum when the work's done (although this might be a while off still!)
Cheers
Andy

 

[Woodchips2]

Toolstation do these loft flooring legs for this problem http://www.toolstation.com/shop/Loft+Fl ... egs/p44016

Regards Keith

Hi Keith.
After five years or so I hope the OP has resolved matters...............easy to miss.
Please pay attention to thread dates/time stamps.
Ta.