new roof and membrane tomorrow, just looked, purlin supoort botched and signs of mould.

[mart321]

Hi all, im due to have work started on my new roof tomorrow. the house is a 1930s semi. been there couple of years now, the membrane is not breathable so moisture collects on it and drips in to the floor and causes the wood from the roof to get wet and its currently looking like it has mould all over it. house still has original tiles so having all those replaced aswell. i am hoping once the new roof and membrane is on this should stop any damp problems. i havnt really spent any time in the loft but ive just been up to clear some stuff out before they roofers turn up tomorrow and i have noticed that my purlins are supported by four bits of wood and two of these are just proppped under and not screwed in or fixed. they seem to be under quite a bit of stress and are on a slight angle so this is causing me a bit of concern.
i am also planning on having the loft converted once the roof is done. it was partly been done by the previous occupants its mostly boarded out with some really old crappy looking fibreglass under. what are peoples onions on me taking this fibreglass out completely? will i need to replace it or will it be best leaving it out so the house can breathe better and heat can circulate to the loft? heres a few pictures

 

[datarebal]

adequate insulation at ceiling level and ventilate the loft space and you wouldn't be getting the condensation issue you currently have.
bump up insulation not reduce it.

 

[Doggit]

The boarding may just be on the original ceiling joists, so couldn't be relied on for the basis of a loft conversion; check the size of them first.

The supports aren't leaning to any great extent, so don't worry about them for now. Looking at the water discoloration on the rafters, suggest to me that it may be due to leaks higher up the roof rather than condensation problems. Has the fibreglass been pushed right up against the soffits, and stopped the airflow into the roof which would have dealt with the condensation issues.

 

[vinn]

Loft conversions need many variables to be in place before any work starts.
Any new roof needs coordinating with the overall loft conversion design or you could find yourself later going over previously done work.

Your purlins are landing on a hip rafter - each purlin seems to be supported by a RS 2" x 4" - you might have much to worry about if the roof is point loaded above the purlins during its renewal.
Have these remedial details been accounted for in any proposed design?

 

[mart321]

The boarding may just be on the original ceiling joists, so couldn't be relied on for the basis of a loft conversion; check the size of them first.

The supports aren't leaning to any great extent, so don't worry about them for now. Looking at the water discoloration on the rafters, suggest to me that it may be due to leaks higher up the roof rather than condensation problems. Has the fibreglass been pushed right up against the soffits, and stopped the airflow into the roof which would have dealt with the condensation issues.

Thats something to consider. Once the roof tiles are replaced and the membrane replaced I think that should be sorted. I'm taking all the insuluation from under the floor and planning on insulating the roof aswell after it's been replaced with kingspan in the summer. So he think that should clear that problem.

 

[datarebal]

condensation without a doubt. It has 1F felt as underlay this certainly aggravates the problem when not properly vented.

 

[mart321]

Loft conversions need many variables to be in place before any work starts.
Any new roof needs coordinating with the overall loft conversion design or you could find yourself later going over previously done work.

Your purlins are landing on a hip rafter - each purlin seems to be supported by a RS 2" x 4" - you might have much to worry about if the roof is point loaded above the purlins during its renewal.
Have these remedial details been accounted for in any proposed design?

The roofer says that these supports have been added after at some point and will add support a bit but are not essential. He has done a few other roofs on this street so I suppose he should know. I just don't get how the purlin would be supported it that 2x4 wasn't there . I expect it runs the full length of mine and my neighbours property. It's suported by the brick partition between our properties but nothing else apart from these Battons?

 

[mart321]

adequate insulation at ceiling level and ventilate the loft space and you wouldn't be getting the condensation issue you currently have.
bump up insulation not reduce it.

I was planning on taking out the old fibre glass insulation at ceiling level and replacing with roof insulation like kingsloft to create a warm loft or roof? I though this was the done thing: either cold loft whereby the heat cannot bypass the ceiling due to the fibreglass insulation , or warm loft whereby there is no insulation in the ceiling so the heat bypasses the ceiling floor but stays insulated in the loft due to the roof insulation such as kingsloft. What happens if you have neither floor nor roof insulation??

 

[Doggit]

Interesting scenario Mart, we had a recent post regarding a similar setup, and there was a disagreement on whether the support was actually supporting the perlin.

You didn't come back on the depth of the ceiling joists, but I suspect you'll end up taking out the fibreglass to allow you access to sort the joists out. Putting insulation back in will help reduce the inevitable heat that rises through the house, but you'll still want 100mm of insulation in between the rafters, and then 50mm of insulated plasterboard across the rafters to stop cold bridging. Essentially, a warm lofts habitable, and a cold loft isn't.

 

[mart321]

Interesting scenario Mart, we had a recent post regarding a similar setup, and there was a disagreement on whether the support was actually supporting the perlin.

You didn't come back on the depth of the ceiling joists, but I suspect you'll end up taking out the fibreglass to allow you access to sort the joists out. Putting insulation back in will help reduce the inevitable heat that rises through the house, but you'll still want 100mm of insulation in between the rafters, and then 50mm of insulated plasterboard across the rafters to stop cold bridging. Essentially, a warm lofts habitable, and a cold loft isn't.

I am unsure on the depth of the ceiling joists as it has been boarded out I will probably find out this week when I look to get rid of all the old fibreglass . So you would suggest 100mm kingspan and then 50 mm insulated plaster board over the new breathable membrane in the room and to remove the the old fibreglass from the ceiling to create a warm loft?

 

[Doggit]

Unfortunately, I've been corrected on my layering system on other posts, but working from the outside, they'll strip the roof and put the breathable membrane down, then batten and tile. Inside, you'd put the 100mm celotex in between the rafters, and then the insulated plasterboard. You'd fill and caps in the celotex with expanding foam, and then use ali tape to seal and joints in the insulated plasterboard. But don't be surprised if I get corrected.

 

[datarebal]

Done thing? Yes of course you can remove insulation from ceiling level if you wish, Foil board between rafters and under the rafters is good.. You need to stop the Warm moist air contacting any cold surface on which droplets will form. (as you currently have on the Underside of the unbreathable felt you have now)
However, you will not get 100mm between the rafters without a 50mm counter batten on or under the rafters.

 

[Ian H]

I have 2 houses, both very similar and one has those supports under the purlins (only 2 though on the front and back ones) and the other house doesn't have them.

Is your new roof having new rafters?

 

[mart321]

I have 2 houses, both very similar and one has those supports under the purlins (only 2 though on the front and back ones) and the other house doesn't have them.

Is your new roof having new rafters?

No new rafters just replacing the small lats which are behind the membrane.

 

[mart321]

Done thing? Yes of course you can remove insulation from ceiling level if you wish, Foil board between rafters and under the rafters is good.. You need to stop the Warm moist air contacting any cold surface on which droplets will form. (as you currently have on the Underside of the unbreathable felt you have now)
However, you will not get 100mm between the rafters without a 50mm counter batten on or under the rafters.

Thanks for the info. Do you think I should have a few vent tiles in the roof?