Advice re insulating over boarded loft

toomuchtrotsky

Hi - we have a boarded loft over one of our bedrooms. The bedroom gets very cold and we would like to add some insulation. 

Novice DIYer - so can I just lay some insulation over the top of the boards? And if so what would be best? Had been looking at wool to ensure breathability - is it worth the expense?

I don’t want to start removing the boards, and the loft will never be used for storage. 

Advice appreciated - thank you!

grumbler

Yes, you can.

And mineral wool is no less breathable than sheep wool, but, I think, much cheaper.

Norman_Castle

If there's a gap between the current insulation and boards more insulation will make no difference. Have you looked under the boards to see what is currently there?

grumbler

Norman_Castle said:

If there's a gap between the current insulation and boards more insulation will make no difference.

Why? I disagree.

Norman_Castle

grumbler said:

Norman_Castle said:

If there's a gap between the current insulation and boards more insulation will make no difference.

Why? I disagree.

Any heat leaking through the ceiling will go around the underside of the boards and escape.

grumbler

If it's one layer of wool placed over another the heat will 'escape' the same way. Boards and some air between then hardly change anything.

FreeBear

Norman_Castle said:

grumbler said:

Norman_Castle said:

If there's a gap between the current insulation and boards more insulation will make no difference.

Why? I disagree.

Any heat leaking through the ceiling will go around the underside of the boards and escape.

In addition, any insulation completely covering the boards will hide the edges from sight. All well and good until someone steps off the edge and goes through the ceiling. If the boards go the full width, then there will be a good draught between boards & existing insulation. Putting a layer on top of the boards will have minimal impact on heat loss as the draught will be carrying the heat away.

Do the job properly. Lift the boards, put down the insulation, and then relay the boards. Shop around, and you'll find the likes of B&Q & Wickes regulalry have fibreglass on offer for around £18 per roll. Not worth the extra expense of sheeps wool unless you value the fuzzy eco feeling.

toomuchtrotsky

Thanks for the advice. There will be insulation under the boards done just a few years ago, does that make a difference? 

The room below has 3 exterior walls, and thought that more loft insulation above would be the quickest way to keep heating costs lower this winter. Am I just wasting my time to put more insulation on top? 

Bendy_House

I agree with Norm; if there is a void between the ceiling and the loft boarding, then it'll almost certainly be (certainly should be...) ventilated to the eaves, so adding insulation just on top of the boarding whilst keeping this void will have little/zero insulating effect.

Fortunately, TMT has confirmed there already is insulation in that space, and hopefully it's nicely filled? In which case, adding even more on top will/should be as effective as adding a further layer of loft insulation would be in any case.

FreeBear

toomuchtrotsky said:

Thanks for the advice. There will be insulation under the boards done just a few years ago, does that make a difference? 

The room below has 3 exterior walls, and thought that more loft insulation above would be the quickest way to keep heating costs lower this winter. Am I just wasting my time to put more insulation on top? 

How thick is the layer of existing insulation ?

If you are already at 250-300mm, adding more is not going to make a huge difference (if any).

Bendy_House

TMT, as FB suggests, there's a good chance that your 'ceiling' is already 'ok' in the insulation department, so I'd be looking at other surfaces too.

For instance, is the floor T&G boards? Is it draughty? If the windows are shut, and you gently open the bedroom door, does it blow open or closed if you open the front door?!

What about the walls - what construction are they, and what side do they face?