Loft Options - opinions please

[Blaggins]

Looking for opinions on how to best solve my loft quandry!

Main requirement: lay boarding to 3m x 1.5m section of centre of loft to improve storage.

Subsidiary Requirement: increase insulation - currently only 70mm of glass fibre (probably original - 1981 built house) between joists.

Contributory factor: Low head height, circa 1.9m in centre (i'm 1.8m tall), which rules out raising the loft floor too high.

Options:

1. Board directly over existing insulation.
2. As 1, but cross-brace (i have some 63mm x 38mm timber already) to create air gap.
3. Replace 70mm wool with 70mm insulation board between joists to double the R value, and board over.
4. As 3, but also using cross-bracing to create air gap.
5. As 4, but also have board insulation between cross braces to bump level of insulation up. e.g. 70mm between joists + 50mm on top = circa 240mm equivalence. Plus the loft boards and it's near enough the recommended level.

Really appreciate anyone's input on what I should do here.

 

[Blaggins]

My Pros/Cons on the options

1. Board directly over existing insulation.

Pros: quick, cheap
Cons: low insulation level, potential for condensation with no gap? (though floor is not above bathroom)​

2. As 1, but cross-brace (i have some 63mm x 38mm timber already) to create air gap.

Pros: still cheap
Cons: low insulation level. Weight of extra timber on loft floor/upstairs ceiling a concern?​

3. Replace 70mm wool with 70mm insulation board between joists to double the R value, and board over.

Pros: Better insulation, relatively quick
Cons: More expensive, Potential for condensation without gap? Do i need to consider the weight of the board insulation resting on the ceiling between the joists??​

4. As 3, but also using cross-bracing to create air gap.

Pros: Better Insulation
Cons: As 3, but also concern around weight of extra timber.​

5. As 4, but also have board insulation between cross braces to bump level of insulation up.

Pros: Best level of insulation
Cons: Expensive, Most effort, Most weight.​

Results-wise, 5 seems the best outcome, but I fear the additional weight is too great, and also that it's overkill for relatively small gain in energy savings - i'm finding very contradictory information around what you actually save by bumping up the insulation!

Either 3 or 4 (depending on if the air gap is needed) feels like the best option, but I just wonder if the board insulation is ok to be rested between the joists, or if it needs additional support somehow.

Though honestly Option 1 would be ideal if the energy savings gains are negligible because I could just get it done asap and move on with my life!

 

[cdbe]

You don't need air gaps. Have you got concerns over the load bearing capacity of the existing joists (which can usually handle a bit of light storage). Insulation will save you money and PIR is better when space is an issue but it's expensive - I would guess you'd need to live there 10 plus years to get a payback compared with just leaving the existing and boarding over, especially for such a small area, in the centre of the house. Wood is a poor insulator so don't put it in if you don't need to. If you can manage to crouch your best bet would be loft legs and 300mm mineral wool.

 

[oldbutnotdead]

6) Chuck 300mm of insulation at the loft floor. Go through the stored stuff- ditch the junk, sell/give away anything useful or store it somewhere you can actually get at it to use it

 

[Blaggins]

You don't need air gaps. Have you got concerns over the load bearing capacity of the existing joists (which can usually handle a bit of light storage). Insulation will save you money and PIR is better when space is an issue but it's expensive - I would guess you'd need to live there 10 plus years to get a payback compared with just leaving the existing and boarding over, especially for such a small area, in the centre of the house. Wood is a poor insulator so don't put it in if you don't need to. If you can manage to crouch your best bet would be loft legs and 300mm mineral wool.

Hey, thanks so much for the reply. I don't have any particular concerns about load bearing, but just am aware it could be a factor. The joists were a little smaller than I expected at around 70mm x 35mm, but I've been told for the size and style of loft that's fine. If it's really somewhere in the ballpark of 10 years to see a benefit in getting the boards to improve the insulation then I think I'll save myself the hassle and expense and just board over what I have then. I imagine within 10 years or so we'd be looking to move.

I did consider loft legs, but it would really make it cramped up there. I know it's not somewhere I spend much time(!), but still, it would make it very small. They also seem fairly expensive when you work out how many you need!

6) Chuck 300mm of insulation at the loft floor. Go through the stored stuff- ditch the junk, sell/give away anything useful or store it somewhere you can actually get at it to use it

Thanks for the response, but our christmas would be pretty sad if we had gotten rid of all our decorations! We don't have too much storage space in the house, so things like that that we won't need often are perfectly suited for loft storage.