can you have too much Loft insulation?

csgohan4

I have my loft insulation to 250mm, is it beneficial to go above this to say 300mm?? my house is currently classed C. Not particularly chasing the EPC ratings, more will it help with heating and bills

Is there a cutoff number (mm) before it becomes counterproductive, i.e increasing damp

FreeBear

csgohan4 said: I have my loft insulation to 250mm, is it beneficial to go above this to say 500mm??

It is a case of diminishing returns. Putting in 100mm where there was none would save (for arguments sake) 50%. Another 100mm would save a further 25%, and a third layer of 100mm, just 12.5%. 200mm on top would only save another 9%...

If you can get loft insulation at a cheap enough price, by all means increase the total to 500mm, but don't expect huge savings. In your shoes, I'd just get a few 100mm top up rolls - That will take you above the current recommended level of 270mm and future proof yourself for a few years.

csgohan4

FreeBear said:

csgohan4 said: I have my loft insulation to 250mm, is it beneficial to go above this to say 500mm??

It is a case of diminishing returns. Putting in 100mm where there was none would save (for arguments sake) 50%. Another 100mm would save a further 25%, and a third layer of 100mm, just 12.5%. 200mm on top would only save another 9%...

If you can get loft insulation at a cheap enough price, by all means increase the total to 500mm, but don't expect huge savings. In your shoes, I'd just get a few 100mm top up rolls - That will take you above the current recommended level of 270mm and future proof yourself for a few years.

does loft insulation need replacing every x years?

FreeBear

csgohan4 said: does loft insulation need replacing every x years?

Not in your lifetime.

I have some loft insulation that was put in some 50 years ago. Only 25mm thick, so hardly worth having. It is still there, all be it with another 200+ of fibreglass on top.

TELLIT01

In answer to the basic question of can you have too much loft insulation - if you have so much that is stops effective airflow and ventilation in the loft space the answer is a definite Yes.

donemedosh

The guides I have read say about 250mm to 270mm is the ideal thickness for loft insulation. But I would say no more than 300mm in a loft as after that it can cause more problems than it cures. Tellit is right if you fill the loft space you restrict the air flow & this can cause damp problems.

Rosa_Damascena

TELLIT01 said:

In answer to the basic question of can you have too much loft insulation - if you have so much that is stops effective airflow and ventilation in the loft space the answer is a definite Yes.

And how much would that be in mm? Going by @FreeBear 's example there will always be some leakage, how much is not enough?

FreeBear

Using a random online calculator - https://www.resurgence.org/resources/heac.html

With no loft insulation, you will lose 28% of the heat through the roof. Put just 100mm cuts the loss down to 6%. 200mm = 3% loss, and 300mm just 2% (assuming no thermal improvements elsewhere). The money spent on extra loft insulation would be better spent elsewhere where there are higher losses such as plugging drafts, fitting decent windows, and wall insulation.

bris

250mm is enough, the EPC should highlight where other improvements are needed.

Usually windows, doors and cavity walls.

Chickereeeee

FreeBear said:

Using a random online calculator - https://www.resurgence.org/resources/heac.html

With no loft insulation, you will lose 28% of the heat through the roof. Put just 100mm cuts the loss down to 6%. 200mm = 3% loss, and 300mm just 2% (assuming no thermal improvements elsewhere). The money spent on extra loft insulation would be better spent elsewhere where there are higher losses such as plugging drafts, fitting decent windows, and wall insulation.

And if you do those other things (wall insulation etc) then the percentage of heat lost though the roof will increase again! 
The total heat lost always adds up to 100%, so reducing the % in one are increases it in another.

FreeBear

Chickereeeee said:

FreeBear said:

Using a random online calculator - https://www.resurgence.org/resources/heac.html

With no loft insulation, you will lose 28% of the heat through the roof. Put just 100mm cuts the loss down to 6%. 200mm = 3% loss, and 300mm just 2% (assuming no thermal improvements elsewhere). The money spent on extra loft insulation would be better spent elsewhere where there are higher losses such as plugging drafts, fitting decent windows, and wall insulation.

And if you do those other things (wall insulation etc) then the percentage of heat lost though the roof will increase again! 
The total heat lost always adds up to 100%, so reducing the % in one are increases it in another.

True, the percentages all add up to 100. The thing to look at is the amount of heat lost in KWh - The more insulation, the less actual heat is lost to the outside.