roof condensation

[Piggery]

2 years ago we had a new slate roof to our 1930's bungalow with tyvek underfelt.No soffit or ridge vents were fitted, we were told tyvek is breathable and vents not required. During frosty weather significant condensation occurs on underfelt, dripping on to loft insulation. Dupont/Tyvek surveyors have visited and told me to seal eaves by pushing insulation in hard. Condensation is now worse. In addition condensation now drips through roof of dormer (flat bitumen roof) staining carpets. Will vents solve this problem. Do I need batten cavity vents as well? Does anyone else have experience of tyvek? Help?

 

[Roofer]

Generally speaking what you have been told is correct - with Tyvek no venting is needed.
However it is only capable of so much!
Condensation is caused when moisture laden warm air meets a cold surface, in your situation I think you need to find out where the warm moist air is coming from and eliminate or reduce it.
Check especially that bathrooms, showers kitchens and utility rooms have extract fans (that are working) and if they are ducted through the roof space there is no leakage from the pipework. Seal around any ceiling penetrations eg holes for pipes or wiring, also seal around loft hatches.
For the amount of condensation you have described there must be a cause.

 

[Piggery]

Thanks for that. I have fastidiously checked for leakages. Kitchen & bathrooms always have extraction fans on when in use. The condensation is worst when there is a frost i.e. when the moisture vapour is frozen into the Tyvek - I guess it is no longer permeable under these conditions. I think I am going to have to install soffit/eaves and ridge vents! Annoying because I feel I have paid twice!

 

[Mr Winston]

has the tyvek been installed with a 15mm drape/sag between the rafters? or is it pulled taute - if so it needs counter battens

just a thought as im sure the Tyvek inspector would of spotted this.

Also if the tyvek felt was improperly stored say left out in the elements for a period, say a month or so, it deteriorates along with its breathable properties - so may not be suitable for installation (or if the roof was felted and then left for a month or so before fixing the covering)

Am i right in assuming that you have a conventional open loft space rather than sloping ceilings in the roof?

 

[Piggery]

Hi Mr Winston. Thanks for your comments. The sag varies between 2 & 20mm - roofing does not apear to be a precise art! However, the Dupont surveyors seemed perfectly happy with the installation and took some samples for testing, which proved OK.

I have a normal open loft space with a flat roofed dormer in the middle. The dormer has sofit vents at the front but the "rear" vents into the loft space, which is now "sealed" by the tyvek. The old roof had no underfelt. I have come to the conclusion that I will have to fit eaves/soffit vents and possibly 2 ridge vents as well. The condensation problem is significant during periods of frost. I assume that the moisture in the tyvek freezes and then it is no longer permeable? My house is a 1930's bungalow, hence the rooms below the loft space are "lived in" not just bedrooms. With the best will in the world it is impossible to hermetically seal an old house, some warmer/ moisture laden air is bound to leak into the loft space. Personally I don't consider an unvented loft space is possible in old houses hence although tyvek may work well in membrane sealed new builds, it is not suitagle for retro-fit!

Any other thoughts you have will be gratefully received!

 

[Roofer]

There are still elements of this problem that are puzzling.
You say that the condensation is worse in frosty (cold?) weather and you think moisture in the Tyvek is frozen, yet you say warm air is getting into the loft - why isn't this thawing the frost?
Secondly you state that in addition condensation is dripping from the underside (?) of the flat roof dormer which infers that this is a new occurence, but the installation of Tyvek would not affect the dormer!
Is there a possibility that the dormer roof is now leaking and introducing dampness into the loft area which subsequently condenses?

 

[Piggery]

Thanks Roofer. The Dormer problem is new, I am assuming that air movement to vent the flat roof used to rely on the draughty loft. Now that the loft area is reroofed with (Tyvek) underfelt I am guessing that there is insufficient air movement to keep the underside of the flat roof condensation free. This new problem occured during the last frosty spell when there was virtually no wind at all i.e. worst case conditions? However, I do have the flat roof contractor coming to check the bitumen & felt, it is 9 years old and coming to the end of its useful life perhaps? I have also had a response from Dupont surveyors, they have taken my problem one level higher and another visit is planned during the next cold spell. I guess the problem will be solved eventually but am I correct in assuming that all loft spaces have a small amount of condensation under certain conditions or should I be aiming to achieve a dry cold loft at all times?

 

[Roofer]

In my, and I believe Dupont's (at least what they admit to) experience, Tyvek performs as it should in all but extreme conditions. These extreme conditions have always been because of new-build drying out therefore producing high levels of moisture.
Dupont's Technical Dept have always been pro-active so I'm not surprised they want a second visit.
Keep us posted.

 

[whiskygalore1]

I have read your comments regarding the above and I am wondering whether it was resolved. I live in a 1930's bungalow and have the same problem. I'm sure that you may be able to seal extractor fans, halogen lights etc to prevent moisture from entering the loft space but what happens when you open the loft hatch? We regulary access our loft for storage as space is at a premium in the house so presumably the loft would no longer be air tight. Did you add vents at the eaves/ridge and did it solve the condensation problem?

 

[JohnD]

//www.diynot.com/forums/viewtopic.php?t=160032

 

[ntiffin01]

Last year my gas plumber got rid of the old fashion immersion tank and replace with a new combi boiler in the attic. But I notice in winter I get condensation builds up in the attic! I live in a 1910 terrace house and do not have underfelt under the roof-slates, therefore the cold slates and a warm boiler builds up condensation during winter!!

I'm told the new underfelt is 'breathable' and I'm thinking of having it put in by a professional roofer. But my question is it "breathable" enough to keep my attic dry? The boiler will be warm through out the winter. Will I need a ridge-vent or slate vent??

I wonder if anyone had similar experience?

NT.

 

[JohnD]

do not have underfelt under the roof-slates,

if you do not have underfelt, you should have reasonable ventilation already. You need to find and rectify the sources of warm, moist air which are rising into the loft.

start by checking that the flue and the condensate pipe both pass outside the loft without any leakage

 

[cornicekurt]

Hi. I've been a slate roofer for 31 years. Slate and Tile roofs are all I do. My family has been in business since 1888.
First of all, let me commend you on choosing to use a slate roof. Nothing more beautiful on a building. Tiles great but not nearly as beautiful as slate.
I was "ordered to use tyvek on a structure once. (architect). They're so smart. Same problem. Its a garbage underlayment for slate, tile, or copper roofs. All these materials are tempramental to the heat and cold. Slate tends to retain both for quite a while. Rain on hot slate tends to create a serious condensation issue also. On winter mornings when the rock is freezing and the sun begins to warm it. you can only imagine whats happening on the backside of your material. Tyvek is to thin and the condensation forms on the deck side of the material. Venting will never eliminate your trouble. I refuse to use the new synthetic underlayments also for that exact reason. I've been in the industry long enough to see these companies come...... Then when their material fails to live up to your expectations they cant be found. Tamco. UL 30# asphalt based felt paper. I've torn off 100 year old roofs and the only place this felt has failed is along the eves and gables where water has either blown into or ice has backed up. Like I tell all my customers. How can you argue with a material that has stood the test of time? We are in a heavy snow region in Michigan and I have many roofs that are burried in snow for 4 months out of the year. No problems. The condensation forms between the slate and the underlayment and it wicks down into the gutter as it is supposed to.
A good roofer may be able to remove your slate and replace your felt without breaking to many pieces.
Sorry about the brutal truth, but it is the truth.