Rafter Insulation — Remove or Keep?

paperclap

Hi all,

Sorry to be blunt about this, but I need a definitive answer to this, and I need it now... because it is causing me a horrendous amount of stress.

We have just moved into our first home. It is a 1955 bungalow.

The roof has concrete Redland tiles and bitumen felt. As the felt is almost 70 years old now, it has more or less all crumbled to dust. Internally, between the rafters is polystyrene insulation held in place with small battens and plasterboard sheets.

We have recently had some roof leaks. Just when I thought they were all sorted, I go up in the loft space today (after last night's rain), test some seemingly wet timber, and it was sitting at the 40% moisture mark. Went up to check the roof externally, but couldn't see any gaps whatsoever.

I have had several suggestions from people (on here) to remove the polystyrene insulation and plasterboard to increase ventilation and allow myself to see if there are any other leaks (as, everything is "hidden" by the insulation). I can remove this all myself, no problem.

However, I don't want the loft space to suffer condensation issues, due to warm/moist air from the living space settling in the cold loft.

Do I remove to increase ventilation and increase visibility? Or, do I keep so as to not create a condensation issue?

Please, please, please give me an answer! Can't tell you how much stress this has caused me going back and forth between removing and keeping! Agh.

plumb1_2

If it was my house I would remove the polystyrene insulation ( fire risk) and plasterboard and allow the roof to get good ventilation. and you need to see why the rafters are getting wet.
As you say it’s got old bitumen felt which is breaking down, also it depends on how long the concrete tiles have been on? As they become porous after 30 yrs etc.
 I need of new felt, battery’s and tiles etc IMO.

casper_gutman

Is the loft just a roof space, possibly with some use for storage? If so, insulating the ceilings with standard mineral wool "loft insulation" is the usual approach.

The main disadvantage of the "warm roof" system you have, with insulation between the rafters, is that it's prone to condensation. A ventilated roof space with air circulating around the rafters should be much better from this point of view.

paperclap

It is only used for storage, yes.

It was my understanding that condensation occurs when warm/moist air comes into contact with cold air. That is why I had thought it may be best to keep the insulation in! 

As it is now, we don’t appear to have any condensation. I’m concerned that removing the insulation will cause condensation. Also, that the insulation is hiding any water ingress issues.

Sure, it could do with new tiles, battens and felt… but had hoped to do that in a few years from now.

I thought tiles being porous was somewhat of a myth? That they could absorb a small amount of water, but it would then evaporate with time. Never actually let in water through the surface of the tile itself.

Bendy_House

laurencewhymark said:

Do I remove to increase ventilation and increase visibility? Or, do I keep so as to not create a condensation issue?

Definitively, without question, 'yes' - remove it.

Insulation between the roof rafters in a standard roof construction and loft area, serves no useful purpose at all, and will very likely cause harm. The rafters under the tiles should be fully ventilated.

Any rain that gets in past the tiles - and in windy conditions this can happen and isn't generally an issue - will risk being trapped behind the insulation and take much longer to be ventilated away. Any rain that gets as far as the surface contact between the polystyrene insulation and the sides of the rafters could well remain there for days before finally being able to dry out under ideal conditions.

And even with this 'insulation', the loft area - especially the undersides of the rafters - will still be the coldest parts of the house, so any warm moist air percolating up from the house (and houses do breathe) will condense out on these surfaces - and will remain there for much longer due to the compromised ventilation. That's a problem.

Putting it bluntly, the draughtier it is up there, the better - because it'll also be drier!

The lack of roofing felt isn't ideal, but usually isn't a problem in itself as it's very much a secondary barrier to rain that might get blown in or leak past a loose or missing tile. In most cases, a bit of rain landing on the timber rafters just isn't an issue, as it'll soon be ventilated dry again in the draughty loft.

Issues arise when the ventilation of the loft space is compromised by, for example, folk stuffing loft insulation tight into the eaves - the main location of loft vents. Or, by covering the undersides - or between - the rafters.

Seriously - let if howl up there. It'll be cold, but dry.

To keep the house warm, just add loft insulation above the ceiling. That's it. That simple. The loft itself won't be warm, but you can still safely store stuff up there - it should remain dry.

There are circumstances where you can add insulation to the rafters, but this needs doing with planning and care. For example, you can line the undersides, even add insulation sheets, but you must still allow a good passage or air above this, from one eave, all the way up and past the ridge, and back down to the opposite eave. Or by also adding ridge vents, or even the required amount of tile vents. Bottom line - it must be vented! So, if you don't do this properly and with guidance, then just leave it as it was designed - uncovered.

paperclap

Thank you so much Bendy_House.

You covered everything and more.

You’ve convinced me to remove it all and let it breathe! 

twopenny

I lived in an edwardian house for years with no loft insulation.
Everything up there was dry including paper. The small amount of heatloss made it an excellent storage space and kept the tiles dry.
On getting the required insulation they put it so there was no ventilation from under the eves and problems ensued.
Take up the polystyrene now and let the roof get ventilated throughout.
Remove the decaying lining - then lay some bubblewrap or polythene across the 'floor' and go up and have a look after rainfall. If there's a leak you will easily find a puddle underneath and know where it is. If none your tiles are fine.
Ideal time of year to do it.
Once sorted lay some new insulation to standard remembering to leave a gap near the eves for ventilation.

stuart45

Remember the old days before insulation with giant icicles hanging down from the roof.

Bendy_House

Ah, but they were dry icicles...

stuart45

Bendy_House said:

Ah, but they were dry icicles...

They tasted good. The dinner ladies at school used a pole to knock them off for us to eat. 

paperclap

Stop scaring me, guys!