Loft - part insulating between rafters?

[zbed]

I'm getting my loft boarded out in anticipation of some light storage. The joists are only 60mm deep (cheap victorian terraced workers' cottage).

Of the thin (60mm) space blanket type insulation that was already there, a section got taken up in one corner 5 years ago when I wanted to put spotlights down into the bathroom.

The guy doing the boarding suggested re-using this by putting it in between the rafters, but it would only reach half way up.

I'm wondering if there's any point to this? Surely the heat would just escape through the uninsulated apex of the roof? He said it'd still help stop draughts round the eaves.

Would welcome others' opinions on this!

 

[PrenticeBoyofDerry]

Have you considered raising your loft level before you board it.
You can run timbers perpendicular to your existing joist thus raising the level for increased insulation depth.
No point insulating between the rafter of the roof pitch, if only for storage.
Leave it uninsulated (roof) and make sure your eaves are also not blocked, allowing ventilation and air to circulate in the loft space or you could end up with condensation problems.

 

[zbed]

Yeah, I did consider raising, but the existing joists are only 6cm deep, I really didn't think putting that much weight on them's a good idea.

Was worried about the condensation problem. Could it happen with space blanket type material? From all I've read it seems to be more pertinant to things like Kingspan?

 

[PrenticeBoyofDerry]

It can happen with any insulations, if air is not allowed to circulate.
What supporting span are the 6cm joists, if you are concerned about any addition weight. I would be more worried about the weight of the loft boards plus storage.

 

[zbed]

Not sure what supporting span means? If you mean distance between each joist it's about 30cm.

There's boards up there now, just not nailed down.

 

[PrenticeBoyofDerry]

I mean the span(length) that the joist cover before they are supported by supporting walls, pillars or beams

 

[zbed]

Ahh gotcha... about 4 meters, max. More like 3.5m I'd say.

 

[PrenticeBoyofDerry]

TBH.
If your joist are 60mm deep, I assume they are only 50mm wide and a span 3.5m between supports.
With the weight of the ceiling and any insulation above, I would forget about boarding it out for storage.