Another loft insulation question

Mendonky

Hi all,

I'm back on trying to replace the insulation in my loft prior to the cold weather and new-born arriving. the loft was full of loose fill (Cellulose?) insulation that is an absolute pain to remove. On getting to the edges of the loft space I have noticed there is a lot of loose fill that seems to be in the space that would be the eaves- I've always been under the impression that I need to leave the eaves completely clear for ventilation and prevent condensation build up. However, From measuring from the light fitting in the room the edge of the room does not correspond to the edge of the loft space from above , so this would leave a 20-30cm section of the ceiling uninsulated where it is angled in the room which seems like a lot of potential to lose heat. the eave seems to hang down a meter below the edge of the loft space.

- do I need to insulate these eaves, and if so what do I do about ventilation? I was considering some kind of solid batt I could trim and slot into each of the eaves spaces as shown in the picture?

The decision to replace the old loose fill was also fuelled by just how dusty and debris filled it was- how important is it to clear all the debris before laying new insulation on top or can i just use the new insulation to "trap" the dust and debris underneath? its causing the job to take 10x longer than expected!
 
Any advice greatly appreciated. pics below for reference.

-S

Chickereeeee

Your joists look quite 'thin' (top to bottom) - what do they measure? Ditto the rafters.

If you are putting in 275-300mm (total) of insulation, I  don't think a bit of dust is going to matter much. Or even some rubble (assuming below joist level).

Is there any external ventilation of the eaves? Soffit vents, or facia strip vents? Is the roof felt breathable?

Mendonky

Chickereeeee said:

Your joists look quite 'thin' (top to bottom) - what do they measure? Ditto the rafters.

If you are putting in 275-300mm (total) of insulation, I  don't think a bit of dust is going to matter much. Or even some rubble (assuming below joist level).

Is there any external ventilation of the eaves? Soffit vents, or facia strip vents? Is the roof felt breathable?

Joists are about 48mm x 65mm (1.9" x 2.55") spaces about 16" apart but there's some super narrow spacing around the edges that will be fun to fill. I'm planning for 300mm total insulation and with the joists being thinner than the 100mm base layer its going to be an interesting patch job around the loft legs.

I had a look after posting this and I can't actually see any obvious ventilation points from the outside. its a very old (1930's ish) house so I do wonder if it had adequate ventilation to begin with? the loose fill ive been removing just seems dirty/ dusty, as opposed to damp/ wet/ rotten but it only had 150mm according to the energy certificate.

Chickereeeee

A 1930s house, unless reroofed, will not have a breathable membrane for the roofing felt then.The other way ventilation can get to the eaves of a property of that age is via the wall cavities. Are these filled, capped or open?

I believe it is the case that the more loft-floor insulation you have, the more likely your are to get roof-level condensation, and so the more important ventilation becomes.

Mendonky

Chickereeeee said:

A 1930s house, unless reroofed, will not have a breathable membrane for the roofing felt then.The other way ventilation can get to the eaves of a property of that age is via the wall cavities. Are these filled, capped or open?

I believe it is the case that the more loft-floor insulation you have, the more likely your are to get roof-level condensation, and so the more important ventilation becomes.

Walls are solid brick unfortunately- no cavity which has been a nightmare for heat retention hence looking at where i can make gains elsewhere!

I've got a roofer coming to Quote me for some tile vents as I cant see any ventilation i the eaves- I'm hesitant to ask about insulating the eves as he might think I'm trying to get free advice!

If theres no visaible vents on the eaves, can i assume it would be fine to insulate them?

DougMLancs

If you decide you want to add soffit vents then you can still insulate by using plastic corrugated trays from the likes of Klober https://klober.co.uk/roof-ventilation/eaves-roof-ventilation/p/loft-vent-tray (other brands available). These mean you can insulate right into the eaves without compromising airflow as it’s directed up over the insulation.

Chickereeeee

DougMLancs said:

If you decide you want to add soffit vents then you can still insulate by using plastic corrugated trays from the likes of Klober https://klober.co.uk/roof-ventilation/eaves-roof-ventilation/p/loft-vent-tray (other brands available). These mean you can insulate right into the eaves without compromising airflow as it’s directed up over the insulation.

The problem there is that OPs rafters  don't look very thick. His joists are only 65mm, and the joists look similar in the photos. Using those trays (30mm thick) only leaves room for 35mm insulation. Better than nothing, but not great. If the rafters are 100mm or more, the trays would be OK, (if you could work out how to fit them. They are designed to be fitted when the roof is built).

I don't have a solution that I could confidently suggest. My last house had a similar construction at the corner, and the gap was filled with insulation with no obvious problem in the 20 years I was there, (But I never looked). Maybe stuff with insulation, but add a length of plastic pipe to each section to ventilate the eaves?

FreeBear

Chickereeeee said:

DougMLancs said:

If you decide you want to add soffit vents then you can still insulate by using plastic corrugated trays from the likes of Klober https://klober.co.uk/roof-ventilation/eaves-roof-ventilation/p/loft-vent-tray (other brands available). These mean you can insulate right into the eaves without compromising airflow as it’s directed up over the insulation.

The problem there is that OPs rafters  don't look very thick. His joists are only 65mm, and the joists look similar in the photos. Using those trays (30mm thick) only leaves room for 35mm insulation. Better than nothing, but not great. If the rafters are 100mm or more, the trays would be OK, (if you could work out how to fit them. They are designed to be fitted when the roof is built).

Have a look at the datasheet.pdf - The 30mm depth is for the grooves. The tray itself sits some 480mm high (depending on the slope of the roof). More than enough to accommodate 300mm of insulation.

Manthorpe also do a similar product that is available in two different widths. Also appears to be quite a bit cheaper than Klober.