Roofing question

[Farmer Giles]

I ran into an old friend today who told me about some problems he had/his having with his roof, and I would welcome any advice/comments from anyone here who has any experience with such matters.

He lives in a bungalow, which was built in the sixties, and about two years ago he started having problems with the roof leaking. He got a firm in, who had been recommended to him, to look at it and they advised a new roof - they quoted him £11,000 for the job, including UPVC guttering, soffits, etc, which he agreed to.

The new roof was fitted 18 months ago. At the time he queried the felt they used, which he said was no thicker than wallpaper - whereas the old felt was quite thick - and he was told that this was what everyone used nowadays and that it conformed to the current British Standard. After the new roof was fitted he started getting quite bad condensation problems, so he got the roofing firm back in.

They said that their roof was perfectly ok - but they didn't know what was causing the condensation problem - although they advised fitting ventilation in the soffit area. He had this done but the problems still persisted. Things got so bad that he called in a surveyor, at further cost, who advised fitting ventilation tiles along the ridge. Again he has had this done (by another roofing firm, having lost confidence in the first), at more cost, but things are no better - in fact the new firm said that the ridge tiles hadn't even been fixed properly, so it seems that the first roofers did a fairly poor job anyway.

It is definitely condensation, there are no leaks, and he - understandably - is at his wits end. He is convinced that the problem is caused by the flimsy roofing felt - the sale of which, we understand, has now been discontinued - and I tend to agree with him.

Can anyone offer any advice or hope whatsoever for this poor chap - who, to add to his worries, has just suffered a bereavement (which is why I happened to meet up with him again)?

[Bypass]

I doubt the felt has got much to do with it. Based on your description, it seems to me that the roof ventilation is inadequate. Give a few more details on the the eaves and ridge ventilation.

[Hugo Nebula]

On Sat, 06 Jan 2007 19:31:28 +0000, a particular chimpanzee named Farmer Giles randomly hit the keyboard and produced:

The 'felt' could have been a breathable membrane (such as Tyvek, Klober, Permoforte, etc).

The traditional way of preventing condensation from causing damage to the fabric of the building is to keep the roof void ventilated. This was (and still is) done by allowing enough space at the eaves to permit air to flow through the roof void. In most roofs this is a continuous 10mm gap to the soffit or the equivalent area. Where the roof void is not a big open space (such as a loft conversion, or a mansard roof), then a gap between the rafters needs to be maintained and ventilated at the top and bottom. The gap at the top should always be less than that at the eaves (off the top of my head I can't remember exactly why, but it is for a good reason). The ventilation at the ridge should be equivalent to a 5mm continuous gap, and the eaves increased to 25mm.

Breather membranes work differently. They are designed to allow water vapour through from inside, but not liquid moisture in from outside. They don't require cross ventilation. What they do require, however, is for the ceiling under to have a vapour barrier to the warm side of the insulation, and any gaps, such as loft hatches, downlighters, etc., sealed. There should also be no ventilation to the eaves or ridge to prevent moist air from the outside being drawn in. I have seen some roofs fitted with breather membranes dripping wet on cold winter days. The manufacturers claim that this will evaporate quickly and doesn't cause any permanent damage.

If one is using these membranes, you should either ventilate it in the traditional way, or seal it and allow it to 'breathe'. One of the problems (IMHO) is that builders/roofers tend to do a mix of both methods, i.e., they think that a breather membrane will allow them to reduce the amount of ventilation without reducing the amount of moisture penetrating the roof void. OTOH, traditional felts were very vapour resistant anyway, so unless the roofers did something to block the ventilation, there won't be any more moisture up there than there was before.

If your friend has now gone down the route of ventilating the roof void irrespective of the type of felt, he needs to make sure it's done properly.

-Have at least a 10mm gap to the eaves, and make sure that the insulation doesn't block the air path (but see above if it has dormers or is a chalet bungalow).

-Seal up any loft hatches with draught-strip, and seal any other holes.

-Ensure that any water tanks have close-fitting lids.

-Add additional insulation to reduce the temperature difference between the felt and the internal air (and save money too).

[Farmer Giles]

Until I see him again I can't tell you much more than I've already told you about the ventilation. He has had eave ventilation fitted, and now ridge ventilation, but the problem still persists. The thing is, prior to the new roof - when he had no ventilation fitted - there were no condensation problems. Can you explain this?

[Farmer Giles]

I'm sure that he told me that, despite having asking about, they didn't fit a breathable membrane - saying that they thought it wasn't necessary.

Fantastic reply, and I thank you for it. I will pass on the information to him.

[Andrew Gabriel]

The old tar felt probably provided plenty of ventilation between the lapped sheets (and maybe though tears if it was torn).

[keith_765]

Cut

It would be interesting to know what the original outer roof covering was and age, example, Natural Slate, Clay Rosemary type. And what as it been replace with now.

As regards of re roofing again, in my opinion, that going over the top. There's got to be a better option. £11,000 sounds a lot, unless its a complicated very large roof.

To have the roof sprayed will be the biggest mistake he'll make. Its condemned by the National Roofing Federation. This method is the last straw for a roof on a building that is shortly being pulled down in the near future, just to keep thing from falling off.

Its got to be a problem with venting.

[AlanG]

Thinner felt. Not as good insulation but probably fits better than the old stuff so doesn't let the air flow. Warm moist air coming up and condensing on roof. Probably needs better loft insulation plus more ventilation. I've noticed new roofs in our road are all fitted with quite large roof vents that were not needed previously.

[Farmer Giles]

I think it had those square interlocking concrete tiles, and I believe that they have been replaced with something similar - I'll clarify all of this when I speak to him again.

I'm not necessarily disagreeing with you, because you clearly know more about roofing than I do, but how do you explain the fact that he never had the problem before with the original, thicker felt? Surely if the inside of the roof lining - felt, membrane, whatever the correct term - is cold then the warm air rising from within the house will condense on that surface? Presumably the only way to stop that would be to fit a membrane that maintains a differential temperature between its two sides?

Something that makes me slightly skeptical about the ventilation solution is what I observe in a wood-shed that I have at the bottom of the garden. This shed - a typical construction for storing logs, open-front, slatted sides, etc - has a roof made of box-profile steel sheets. At this time of the year, ie when it's cold, the inside of the roof fairly drips with condensation. Now this shed is almost as well ventilated as the middle of a field but, because of the inevitable temperature difference between the interior and exterior surfaces of the roof, moisture quite naturally condenses on the inside.

I have a similar problem in my small workshop, even though the door is left open all the time, which has the same type of roof as the wood-shed. I had decided some time ago that next summer I would take the sheets off, fit some plywood or chipboard sheets, and refit the box-profile sheets on type.

I'm pretty sure that will solve the problem, but what I am doing is surely analogous to fitting a thick insulating membrane on my friend's roof?

[Farmer Giles]

Thanks, I think your explanation about the felt is probably correct.

[keith_765]

CUT

Sorry to inform you, the old bitumen felt lets less draft in that the newer lighter thinner ones do. Bitumen felt dries out goes brittle, with no movement and on the over laps bond together.

[keith_765]

Your mail as been forwarded on to another group. If you want to take this up to see what other professional, like my self can come up with. Follow it on free.uk.trade.roofing

[Farmer Giles]

Thanks once again, Keith, I have subscribed to this group and will follow any replies with interest.

[keith_765]

I've tried to give as much info as I can on your behalf to free.uk.trade.roofing . Please feel free to add as much more as you can to help resolve your friend problem.

One more thing that might help is, as the loft ceiling insulation been altered while re roofing. can you give any details. On both groups so I don't have to re post.

Is there a personal first name Mr Giles ?.

[Farmer Giles]

Giles will be fine, thank you Keith. I will post this to both groups, as you request.

The loft insulation has not been changed in any way. To answer some of the other points raised: I'm not completely sure why the roof had to be replaced, he told me that there had been problems with leaks and that a new roof was advised. He did tell me the type of tiles that were fitted, but I have forgotten the exact name - they were definitely Redland something or other, and I think the name 'Wold' came in to it. The new tiles were almost an exact match for what was on there previously.

The condensation problem affects the loft space only, and there were no problems before re-roofing. The property is in Birmingham, and was built in the early sixties.

[keith_765]

If Redland or Marley tiles have been used, both companies do have a technical departments and technical support that will answer any question. I have spoken to Redland for there advice but not knowing the full history I can't answer all there questions. They want to know if there as been a specification, type of tile, pitch of roof and it would be handy to have the surveyors report ready. Redland Technical on 08708702595 Wait for a representative to answer, you may have to wait for one to be free. If its Marley tiles then phone Marley, If you have problem finding the phone numbers let me know.

[Farmer Giles]

Many thanks, Keith, this is very helpful and obliging of you. I did post a reply to an earlier post of yours, but it hasn't appeared on my server so I will repeat it here:

"Keith, I will be speaking to my friend later on today, and I will try to find an answer to all your questions - why the re-roof, etc. Redland Stonewolds were the type of tile that he said. He did also tell me something about the new tiles that were fitted - but largely that the roofer used tiles that cost about £2.30 each when he could have got something similar for less than a pound.

I have already passed on your advice about the foam - which was actually my suggestion (blushes deeply), and that idea/thought has now been firmly abandoned. I am very grateful for your considerable help here. It is not my problem, but my friend is going through a bad time at the moment and I would like to help him as much as I can.

Giles"

[Farmer Giles]

I spoke to my friend again this evening and asked him for more information about his roof. He said that the reason for the re-roof was because there had been a few problems with leaks which had apparently been difficult to locate, also some of the rafters had bent under the weight of the tiles and needed replacing. In addition to this some of the felt had also rotted away. The tiles themselves were in reasonable condition, but he decided to have new ones fitted when they stripped the roof.

He said that the new felt/membrane that the roofers fitted was called 'Cromar Protect 1F'. He also tells me that in the last few days he has had some additional ridge ventilation fitted, so now it is a matter of waiting some time to see if this helps the roofspace dry out - a surveyor looked at the problem yesterday and said that the roof timbers, and the brickwork of the chimney that comes up through the loft, had very high moisture levels.

I think that I've covered everything.

Cheers - Giles

[keith_765]

CUT

Right, I've been on the www site of 'Cromar Protect 1F'. It states "a non breather membrane that requires venting" There's is your answer to the problem. The only thing you haven't mention or didn't ask is, what pitch is the roof. If as I think, its a low pitch roof, this will add to the problem, extra vent required. Lets hope that the additional vent your friend has had put in is a success.

[Farmer Giles]

Yes - sorry, I forgot to say - the roof does have a low pitch. As you said, we will now have to hope that the extra venting sorts the problem out.

Many thanks for your advice, you have been exceptionally helpful.