Loft Insulation and Ventilation

[LoftyAmbition]

I have spent the weekend laying 200mm glass fibre insulation between the joists of my loft. I plan to cross-lay a further 100mm as soon as Homebase have another 10% day! (or maybe not, looking at some other posts)

My house was built in the 1970's and is chalet(ish) style, so that i have no soffits or facias and there is no ventilation gap between the base of the rafters and the house walls.

The roof covering is concrete tiles over felt, the felt originally had a fibreglass backing.

I am concerned about condensation problems in the future,as I have no soffits or facias to put ventilators in, i do have some vertical wall space to add larger ventilators to, would this be sufficient? can these be added from inside? Any makes? I don't want to add ridge ventilators if i can help it

Or am i worrying unnecessarily? is it possible that the felt is in some way 'breathable'?

 

[masona]

I have spent the weekend laying 200mm glass fibre insulation between the joists of my loft. I plan to cross-lay a further 100mm as soon as Homebase have another 10% day! (or maybe not, looking at some other posts)

Adding another 100mm insulation is a waste of time and no real cost saving.

My house was built in the 1970's and is chalet(ish) style, so that i have no soffits or facias and there is no ventilation gap between the base of the rafters and the house walls.

Any picture (?) as you say you have no soffits or facias.

The roof covering is concrete tiles over felt, the felt originally had a fibreglass backing.

Have you still got fibreglass backing in the roof rafter ?

I am concerned about condensation problems in the future,as I have no soffits or facias to put ventilators in, i do have some vertical wall space to add larger ventilators to, would this be sufficient?

Yes, 1 on each opposite side would give you a crossflow of air.

can these be added from inside? Any makes? I don't want to add ridge ventilators if i can help it

No, you need be outside as well as inside and for safety reason, fallen brick can killed someone.
A ridge vent is not too difficult to do, the easiest way is to use roof tiles vent by cutting the roofing felt correctly behind it.

is it possible that the felt is in some way 'breathable'?

They are available but have a shorter life.

 

[LoftyAmbition]

Dear Masona,

Thanks for the speedy reply, the answers to your questions are:-

Adding another 100mm insulation is a waste of time and no real cost saving.

- Had read this on other posts, but many 'energy saving' websites say 270mm is a minimum.

Any picture (?) as you say you have no soffits or facias.

I am at work, so no pics, but the house is two story, and the roof-line comes down to ceiling height on the ground floor. There is no ventilation at this point, i have checked all round, because one of the reasons for sorting the loft was 30 or so years of various bird (and mammal) nesting.
There were some very small holes, at joins etc. but these were not for ventilation, and i have plugged them with chicken wire.

Have you still got fibreglass backing in the roof rafter ?

Bobby Charlton had a better covering! it has mostly come away, i don't suppose it was ever more than 50mm.

Yes, 1 on each opposite side would give you a crossflow of air.

T-shaped roof (therefore is three OK?), rule of thumb about size?

No, you need be outside as well as inside and for safety reason, fallen brick can killed someone.
A ridge vent is not too difficult to do, the easiest way is to use roof tiles vent by cutting the roofing felt correctly behind it.

It is a detatched house, with land around, the walls are block, so i'd probably drill holes and push through, but i suspect a frontplate is needed so can't avoid a ladder!

Roof tiles vent sounds good, are the any makes, names you could suggest?

Thanks for the help, so much for a weekend job!


Mike

 

[masona]

Adding another 100mm insulation is a waste of time and no real cost saving.

- Had read this on other posts, but many 'energy saving' websites say 270mm is a minimum.

I'm afraid it's the government red tape again.

Any picture (?) as you say you have no soffits or facias.
I am at work, so no pics, but the house is two story, and the roof-line comes down to ceiling height on the ground floor. There is no ventilation at this point,

Okay, where are the gutter fitted to ? A picture would be great if you can.

Have you still got fibreglass backing in the roof rafter ?
Bobby Charlton had a better covering! it has mostly come away, i don't suppose it was ever more than 50mm.

You can only have roof rafter or ceiling insulated but not both.

Yes, 1 on each opposite side would give you a crossflow of air.

T-shaped roof (therefore is three OK?), rule of thumb about size?[/quote]
The more the merrior !

Roof tiles vent sounds good, are the any makes, names you could suggest?

They do many type, see here

 

[masona]

Just remembered I fitted a Velux window for my next door neighbour because he wanted to.......

1, To let the daylight in, got fed up with extension light.

2, Open the window fully on a hot day to let hot air out.

3, Nightvent open all the time for ventilation or you could leave it 10% open which come with a internal security bolt.

 

[LoftyAmbition]

Dear Masona,

Okay, where are the gutter fitted to ? A picture would be great if you can.

meant to bring a picture to work, forgot.. The rafters extend about 18 inches beyond the wall, and the guttering fixes to the rafter ends. Sounds odd i know, but it is a one-off country style house.

You can only have roof rafter or ceiling insulated but not both.

The original insulation has deteriorated to such an extent it can be ignored. I had toyed with the idea of fixing the insulation to the rafters, it would have been the obvious answer, as i assume the house was designed with a warm loft. I have read that warm lofts are more attractive to rodents and birds, this has definitely been the case, and may still be, but i have put down a lot of bait. Due to the style of the house, keeping them out of the loft isn't easy. I also see little point in heating a part of the house that's used to store a couple of suitcases.

I have thought about tile vents over night, but i can see a lot of practical problems, not least access to the roof, and the fact that i don't much like heights. I think i will go with vents in the wall ends, if i get the right style, it should be possible to drill and chisel the holes from inside, pull the exterior plate up on string, and fix from inside.

Thanks for your help, it's a times like this i miss my dad, he was my DIY consultant for 20 years until he passed away last year.

Mike

 

[masona]

I have thought about tile vents over night, but i can see a lot of practical problems, not least access to the roof, and the fact that i don't much like heights. I think i will go with vents in the wall ends, if i get the right style, it should be possible to drill and chisel the holes from inside, pull the exterior plate up on string, and fix from inside.

You can fit Velux window from inside but you may find it easier to put in air-vent method instead.


Sorry to hear about your dad, I too miss my dad who was a brilliant writer and wrote comedy plays and did some for "The Goons". I was young when my dad died but I could do with some help with my writing now !