Loft Insulation (real world returns)

[padstar]

I have an early 1900's house which we have fully refurbished including insulating the external walls.

The loft has been cleared, rewired and hoovered out and now i need to insulate it. I want to board the loft for storage.

The roof joists are 100mm and unless i get a large return from an investment I dont really want to go to the bother of cross joisting/loft legs.

With that in mind the easy option is 100mm loft quilt then board on top.

In reality what am i loosing by only having 100mm of insulation in the loft. From what i have read the 1st 50mm does most of the work, the 2nd 50mm less and then everything over that is greatly reduced. Is that the case.

Bearing in mind teh house was originally solid un-insulated walls with 20mm max loft insulation we will be greatly bettering no matter what we go with but was just curious how you all see loft insulation and the benefits above 100mm quilt.

 

[noseall]

Any gaps in your 100mm will have a severe detrimental effect without the benefit of 200mm above. And then there is the cold bridging through the joists themselves. How will you mitigate that?

 

[Notch7]

I have an early 1900's house which we have fully refurbished including insulating the external walls.

The loft has been cleared, rewired and hoovered out and now i need to insulate it. I want to board the loft for storage.

The roof joists are 100mm and unless i get a large return from an investment I dont really want to go to the bother of cross joisting/loft legs.

With that in mind the easy option is 100mm loft quilt then board on top.

In reality what am i loosing by only having 100mm of insulation in the loft. From what i have read the 1st 50mm does most of the work, the 2nd 50mm less and then everything over that is greatly reduced. Is that the case.

Bearing in mind teh house was originally solid un-insulated walls with 20mm max loft insulation we will be greatly bettering no matter what we go with but was just curious how you all see loft insulation and the benefits above 100mm quilt.

I put 120mm celetex in my loft - I packed the 100mm joists with some OSB strips which was enough - I’m thinking of adding 50mm Celetex over the top to stop thermal bridging.

 

[padstar]

Good points raised. Realistically though will it make a noticeable difference. If we are talking £50 a year more on heating I can live with it as it will give me benefits in storage. If it will cost far more than that and leave me with a cold house I will have to go for additional layers of quilt. Just trying to gauge the real life noticeable cons of only installing 100mm

 

[HERTS P&D]

Just cross joist a section of the loft that you want for storage. That way you can have 250mm of insulation under the boarding and have the rest of the loft up to 300mm.

Andy

 

[^woody^]

I have a canopy roof above an unheated porch and attached conversion - which is heated but never really warm and cooled quickly. These face south and get the sun.

During some reroofing I increased the 100mm insulation to 400mm and the difference is astounding.

Winter night temps of the porch went up from around 12° to around 17° and never feels cold now.

I don't have temperature measurements for the room, but it is warmer nowadays, you can definitely tell it warms up more via the window when it's a cool but sunny day.

I thought I would get overheating problems with the porch in summer, as it has no ventilation except the front door, but to my surprise it stays relatively cool.

So anecdotally, the increase in insulation has made a significant difference.

 

[Deleted member 292770]

You don’t want to waste money so you attached insulation outside your house.
Legend.

 

[padstar]

Ok Cross batten it is then

 

[Deleted member 292770]

I put 120mm celetex in my loft - I packed the 100mm joists with some OSB strips which was enough - I’m thinking of adding 50mm Celetex over the top to stop thermal bridging.

In today’s money a three bed semi would cost you over 2.5k.