Loft Insulation - A Big Con?

[camel307]

I have debated installing loft insulation......

My house is a 4 bed detached and i pay £100 per month for gas and electric. Joists are 70mm so putting insulation in between joists is futile and impossible as thinnest width i can find is 100mm. And i am not stupid enough to start raising boarding etc....no way mate!

Currently there is a very thin layer on underside of felt. I have contemplated topping up the rafters (90mm) with insulation. The scare mongerers waffle on about a 50mm ventilation gap. 'If you dont do it, you will be plaugued with condensationit will be raining in the loft........how....why????
What is the difference, these vast molecules and gallons of water cant escape today as the felt is non permeable...so where does it go? I imagine, through the eaves - along with all my heat! So, if i insulate the rafters...what will change...the gallons of water per day will vent through the eaves and so will my heating continue to do so! Why should i get condensation - this is totally illogical - the felt is non permeable - the insulation doesnt change this!

My neighbour who has an identical house has followed the regs and applied insulation to 300mm thickness (more than the 270 defined by regs). His monthly gas/electric bill has not changed (he installed the insulation 2 years ago) and is as much as mine! Also, on a frosty, snowy morning his snow clears at the same time as mine - literally within the hour! Surely, thats enough to tell us its a BIG CON! But i did see 4 pigeons on my roof when it last snowed while the neighbours roof was vacant....they were toasting marshmallows....

I am still intrigued to hear how the wool causes condensation if installed along rafters. I think some people LOVE to over think things!!!! Makes them sound clever.....

 

[JohnD]

Joists are 70mm so putting insulation in between joists is futile and impossible as thinnest width i can find is 100mm.

If you are serious, and you have no loft insulation, you are crazy.

 

[Diver Fred]

When I lived in a 'modern-ish' (1985) I insulated the loft, twice! First time between the trusses and find that I had just many cold spots and some dripping condensation. That lasted 3 years before we took it out and started again.
2nd time I fixed 50mm PIR on the underside of the trusses and taped over all the joins. At the edges used (carefully) cut sections of PIR to fill the gap between the ceilings and the bottom of the PIR. Have a thickness of blanket insulation over the ceilings. I
Does it work? Well the loft is definitely warmer and no drips. Has it affected the energy consumption? Maybe. Snow does not melt away as quick as neighbours roofs. Storage in loft is better. No drafts though loft hatch.
What I do notice is more condensation on DG windows!

I sure what would help is a form of heat exchanging ventilation in the house. Stopping heat loss does also stop or reduce ventilation.

 

[mikeey84]

You can insulate a draughty house until the cows come home, but if you do not draught proof it, you will still feel cold