best insulation for tight spaces in eaves, need to leave gap

[Zelfer]

Hi.

Following some work I'm the loft this weekend, id noticed that the eaves were all blocked up, so there was no air flow at all.

I've pulled it all back to give 10cm of clearance, but this means I've got approx 4 inches of plasterboard that has no insulation on it at all.

Therefore I'm looking at something that I can use that has the highest possible insulation but can be prevented from blocking the eaves/soffits, so thinking possibly some polysterene sheeting cut to size to fit the angle of the roof and tacking it to the joists with glue, and then rolling out insulation up to that, or shaping some 4mm wire mesh to meet the rafters, therefore preventing it being pushed into the air gap.

Are there any other possible options that people suggest?

 

[foxhole]

Don't remove it compress with offcuts of plasterboard.You only need a small gap for ventilation.

 

[AronSearle]

As foxhole has said, plasterboard or some other offcut is easy, and this does the job.

The best thing to do would also be the biggest pain in the rear to fit.

A rigid insulation slab about 400mm long which then butts to mineral wool, like you have considered would be best. firmly attache it down and tight between the rafters. This would stop airflow through the insulation caused by ventillation airflow, which happens with mineral wool and locally reduces it's ability to insulate near the eaves contributing to cold bridging at internal ceiling corners (you still leave a gap above for airflow).

I did this to stop condensation forming in ceiling corners. If you don't have this issue then it's probably not worth it, unless like me you are OCD about these things and have some free spare rigid insulation.

 

[Zelfer]

As foxhole has said, plasterboard or some other offcut is easy, and this does the job.

The best thing to do would also be the biggest pain in the rear to fit.

A rigid insulation slab about 400mm long which then butts to mineral wool, like you have considered would be best. firmly attache it down and tight between the rafters. This would stop airflow through the insulation caused by ventillation airflow, which happens with mineral wool and locally reduces it's ability to insulate near the eaves contributing to cold bridging at internal ceiling corners (you still leave a gap above for airflow).

I did this to stop condensation forming in ceiling corners. If you don't have this issue then it's probably not worth it, unless like me you are OCD about these things and have some free spare rigid insulation.

Thanks.
Unfortunately I was up in the loft trying to sort out the insulation as I've suffered from mould caused by condensation in the corners which has run down the roof felt...

Im trying to work out what to spend my free green deal money on, and loft inflation needs a top up/ replace, but want to know if it's worth me doing this instead and then getting BG to do the new install for free outside the gd.

 

[Zelfer]

Don't remove it compress with offcuts of plasterboard.You only need a small gap for ventilation.

My understanding is compressing it can significantly reduce its effectiveness due to reducing the air in it. I have to buy stuff anyway to build this up, so was thinking mesh rather than plasterboard as that could be easier attached at the sides of the rafters with staples.

 

[foxhole]

Don't remove it compress with offcuts of plasterboard.You only need a small gap for ventilation.

My understanding is compressing it can significantly reduce its effectiveness due to reducing the air in it. I have to buy stuff anyway to build this up, so was thinking mesh rather than plasterboard as that could be easier attached at the sides of the rafters with staples.

You would only compress a short section and the effects on insulation would be negligible.

 

[Zelfer]

Don't remove it compress with offcuts of plasterboard.You only need a small gap for ventilation.

My understanding is compressing it can significantly reduce its effectiveness due to reducing the air in it. I have to buy stuff anyway to build this up, so was thinking mesh rather than plasterboard as that could be easier attached at the sides of the rafters with staples.

You would only compress a short section and the effects on insulation would be negligible.

As it's already a cold area and with ventilation next to it and being prone to condensation,, I was wondering if it's worth going with something like the radiator backing foil bubblewrap then some shaped xps.
That way I can keep the insulation total r value, but not take up as much space.

 

[foxhole]

Cure for condensation is good ventilation.

 

[Zelfer]

Cure for condensation is good ventilation.

Yep. Getting mushroom vents installed in the loft, meaning colder loft, meaning more insulation over living room area, hence need to get good insulation without blocking up eaves.

 

[AronSearle]

Cure for condensation is good ventilation.

Go away.

 

[Sam Gangee]

Short lengths of PVC guttering pushed into the eaves will allow air movement without that air impinging on (or going through) the insulation.

 

[misterhelpful]

Get a few rolls of this kind of thing:

https://www.roofingsuperstore.co.uk...-roll-panel-eave-ventilator-2-x-6m-rolls.html

It's designed to be fitted before the felt goes on but you can retrofit it by cutting it into pieces to fit between your rafters from the inside. Pull back the insulation (as you have already done) slide the venting pieces into position and push the insulation back up tight to it, holding them in place. It should sit tight against the felt and give ample ventilation to eliminate condensation > mould > rot > new roof!!

 

[Zelfer]

Get a few rolls of this kind of thing:

https://www.roofingsuperstore.co.uk...-roll-panel-eave-ventilator-2-x-6m-rolls.html

It's designed to be fitted before the felt goes on but you can retrofit it by cutting it into pieces to fit between your rafters from the inside. Pull back the insulation (as you have already done) slide the venting pieces into position and push the insulation back up tight to it, holding them in place. It should sit tight against the felt and give ample ventilation to eliminate condensation > mould > rot > new roof!!

Thanks for that, looks perfect, especially if I can staple 4mm galv mesh to the top of them to try and stop the furry invaders getting in as well!

Definatley looks easier than trying to cut 60 odd polystyrene angles to 270mm tall.