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Condensation on attic felt - possible lack of air circulation due to blockages

  • 03-02-2021 8:46pm
    #1
    Registered Users Posts: 272 ✭✭ electrofelix


    Got the attic insulation upgraded about 18-20 months ago, and I'm seeing some issues with moisture.

    Reported to the installer about 3 weeks ago around the a couple of very cold days that I had seen noticeable droplets of water covering the underside of the felt in the attic and the items I had put up there recently for storage felt damp.

    They looked and reported that it was likely due to the extraction unit in the bathrooms not properly venting out. The ducting runs to the soffit but there was no dedicated vent installed in the soffit for it. So while it sits over an exhaust there is likely some leakage.

    Bought and ran a desiccant dehumidifier to dry out the attic over a few days. Over the next couple of weeks have not used the extractor and relied on just opening the bathroom windows. I've checked again and the droplets are back and they are covering areas that are the opposite side of the house from where the bathroom is, so I'm thinking that it might not be due to the extractor fan and ducting.

    Taken some pictures and to my untrained eye I'm thinking these suggest there is enough of the insulation blocking air flow from the soffits to cause an issue. These are photos looking at front and back only rather than the side, since all of the vents were added to the front/back.

    Before I go back and start another conversation with the installer I'd like to see if my understanding makes sense or make sure I'm checking this the right way rather than ending up in a dead end argument. Essentially I'm using leakage of light from the outside through the vents in the soffit to gauge how easy it will be for air to circulate to vent the attic.

    View of the back rafters starting from the adjoining wall (just stitched the photos together), first one seems alight, but from then on there seems to be quite a few have something sitting down near the soffit with relatively little clear daylight at the end of any:

    NBPSWGp.jpg?1
    full size back-view.jpg

    Front view of the house to help show where the dormer feature will appear:

    cMfEW97.jpg?1
    full size 20210130_161107.jpg

    Front rafters skipping by one because the chimney makes access to a little awkward, as you would see it if you were in the attic. So dividing wall to house next door is to the right, starting with one section over. So I'd expect some blockage on the first image on the right from the dormer feature also impacting the next 2 sections. However I'd imagine I should be seeing some daylight coming through the vents at the soffit on the final 2 sections on the left as well and I'm not seeing any suggesting to me that it's going to be difficult for air to vent freely.

    37NEiiL.jpg?1
    full size: front-view.jpg


    Am I incorrect in expecting to use light leakage based on the number vents to be able to gauge whether or not that air can circulate freely?


Comments

  • Registered Users Posts: 252 ✭✭ Biker1


    In order for condensation to occur in the first place there is warm moist air meeting a cold surface. It looks like there may be adequate ventilation but unless you address the air infiltration coming up from the interior of the house there will always be a chance of condensation build up.


  • Registered Users Posts: 1,246 ✭✭✭ dathi


    They looked and reported that it was likely due to the extraction unit in the bathrooms not properly venting out. The ducting runs to the soffit but there was no dedicated vent installed in the soffit for it. So while it sits over an exhaust there is likely some leakage.


    fix that for a start


  • Registered Users Posts: 272 ✭✭ electrofelix


    dathi wrote: »
    They looked and reported that it was likely due to the extraction unit in the bathrooms not properly venting out. The ducting runs to the soffit but there was no dedicated vent installed in the soffit for it. So while it sits over an exhaust there is likely some leakage.


    fix that for a start

    Deliberately have not used the extractor since it was mentioned in order to confirm whether it was primarily the cause.


  • Registered Users Posts: 272 ✭✭ electrofelix


    Biker1 wrote: »
    In order for condensation to occur in the first place there is warm moist air meeting a cold surface. It looks like there may be adequate ventilation but unless you address the air infiltration coming up from the interior of the house there will always be a chance of condensation build up.

    Are you saying that not using the extraction system is insufficient to avoid the warm moist air coming up from the interior of the house? Otherwise I'm not sure what else there would be. The attic access has a seal and insulation on it as well, and the water tanks are covered. I wouldn't have thought that much warm air could be pulled up from the end of the ducting without the extractor running.


  • Registered Users Posts: 2,544 ✭✭✭ MicktheMan


    Are you saying that not using the extraction system is insufficient to avoid the warm moist air coming up from the interior of the house? Otherwise I'm not sure what else there would be. The attic access has a seal and insulation on it as well, and the water tanks are covered. I wouldn't have thought that much warm air could be pulled up from the end of the ducting without the extractor running.

    Airflow from house to attic isn't essential for issues to arise. Water vapour partial pressure difference (aka air temperature difference) is enough to pump water vapour through most general building materials. Having an open channel such as a duct just makes it easier.


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  • Registered Users Posts: 272 ✭✭ electrofelix


    MicktheMan wrote: »
    Airflow from house to attic isn't essential for issues to arise. Water vapour partial pressure difference (aka air temperature difference) is enough to pump water vapour through most general building materials. Having an open channel such as a duct just makes it easier.

    Sounds like you are suggesting that I need to take some plastic and tape shut the extractor fan inlets if I want to be eliminate the extractor fan setup as the cause of the moisture appearing in the attic?

    Or is that even sufficient to confirm?

    My understanding was that moisture (mostly sweat) would penetrate ceilings and eventually reach the attic, and due to the extra insulation this would make the surfaces even colder requiring better air flow and ventilation in the attic to ensure the moisture was carried away outside otherwise it would condense on the surfaces within the attic. So I assumed that if you couldn't see that there was a clear path for the air to move freely through the soffits past the insulation (by using light for a proxy where the there are enough vents), then it would be unlikely it would be able to carry away enough of the moisture.

    If it's not possible to be reasonable sure based on that general observation, is there another relatively straight forward way for me to tell without resorting to something like a smoke machine? I'd like to eliminate it as quickly as possible, and as we move towards spring/summer I'm guessing it'll become less of an issue until it potentially reappears in late autumn.


  • Registered Users Posts: 272 ✭✭ electrofelix


    Blocked the inlet vents until the problem is fully resolved, just relying on opening windows for now. Also got a set of remote humidity/temperature sensors, put the 3 of them in the attic with one additional one in the display unit in the kitchen and I've tracked the numbers over a couple of different dates. They helped rule out warm air from the bathrooms going up there after a shower due to a lack of much change in humidity over the next hour, but otherwise I'm not entirely sure what the numbers mean. Do they mean it's working as well as it should, or do they mean there is an issue with air circulation?

    Date|Main Unit (Kitchen)|Attic North|Attic West|Attic South|Outdoor
    01/04 @ 4pm|23.6C / 50%|17.9C / 77%|20.2C / 73%|19.2C / 72%|14C / 72%
    02/04 @ 1.30pm|22.7%C / 49%|14.6C / 78%|16.4C / 75%|17.9C / 70%|12C / 58%
    02/04 @ 6.30pm|20.4C / 43%|20.4C / 69%|24.2C / 61%|22.2C / 62%|14C / 53%
    04/04 @ 9pm|19.6C / 46%|20.6C / 69%|23.2C / 58%|21.5C / 61%|forgot
    01/05 @ 4pm|19C / 43%|23.4C / 52%|25.1C / 48%|24.8C / 41%|12C / 52%
    02/05 @ 11.30am|20.2C / 47%|14.2C / 59%|14.8C / 61%|17.4C / 52%|11C / 55%


    Generally I can understand some variability should exist, with the south facing part of the attic getting most of the sun during the day so it should warm up a bit more, and west getting a bit in the afternoon and evening. And the temperatures would impact the humidity registered, with higher temp resulting in lower humidity.

    But on 1st May at 4pm, the west facing part had both a higher temp and higher humidity than the south facing side?
    There are times with 3.5C difference between West and South on the 2nd April with a 5% humidity difference, but a 2C diff later at 9pm makes for only a 1% humidity diff? In general the north side is cooler and higher humidity except for 2nd May, where it's the West side but only marginally.

    Do these mean anything or is since the temperature isn't getting ridiculously high when the sun is out, it means there must be reasonable air flow? It feels dead to me when I go up there, while I was expecting a bit of a draft.


  • Registered Users Posts: 10,928 ✭✭✭✭ Calahonda52


    The proper way to have done this is to use ventilation baffles.
    The simplest solution is to fit some roof tile vents, more mula yes but will make sure you have positive air circulation
    I see very few vents in the soffit, I assume they are downlighters
    the vents need to be equivalent to a 10mm strip all the way along the eaves, front and back

    so 10mm by 1000 mm ( 1m length of eave) is 10,000mm2 and
    IIRC, the vented roof tiles are that size so one per meter, they need to be, both sides, along the bottom and some ups near the ridge, I forget the exact rules now :)


  • Registered Users Posts: 272 ✭✭ electrofelix


    The proper way to have done this is to use ventilation baffles.
    The simplest solution is to fit some roof tile vents, more mula yes but will make sure you have positive air circulation

    Thanks, ventilation baffles appears to be the keyword that I needed to know about.

    Allowed me to find the following thread post: https://www.boards.ie/vbulletin//showthread.php?p=112576438#post112576438

    Is this something that fitters should be using to meet SEAI requirements for the grants, or is this a case of not required by the minimum reqs, so only if you knew beforehand to ask for the quotes to include fitting them?
    I see very few vents in the soffit, I assume they are downlighters
    the vents need to be equivalent to a 10mm strip all the way along the eaves, front and back

    so 10m by 1000 mm is 10,000mm2 and
    IIRC, the vented roof tiles are that size so one per meter, they need to be along the bottom and some ups near the ridge, I forget the exact rules now :)

    Looks like they are these:
    https://www.nwa.ie/products/kytun-roof-ventilation/soffit-ventilation/circular-soffit-vents/klober-circular-soffit-vents/

    Assuming 37.5mm radius, allow for some loss, at 30mm radius I'm coming up with 2827mm2 per vent, which with 10 front and back gives 28274mm2, so I'd guess there is possibly enough on the front and back, if the airflow was clear. There are only a couple of the small strip vents along the west side of the attic, I wonder if that could account account some of the lack of circulation, but it does seem that probably the main issue was the lack of the baffles to keep the ventilation path clear (as well as away from insulation it appears).


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  • Registered Users Posts: 272 ✭✭ electrofelix



    Do you mean I shouldn't bother trying to look at fixing the insulation partially blocking the air circulation at the eaves and instead fit roof tile vents to properly ventilate the attic?

    Or were you referring to the need to fix the venting of the extractor and rather than use something like https://www.amazon.co.uk/gp/product/B00GRSSAQK/ref=ox_sc_saved_title_5?smid=A2DAIRTE1JXFQ3&psc=1, I should use a tile vent. The south and west attic roofs near the bathrooms would be exposed to prevailing winds and near the coast so wasn't confident that it wouldn't just get blown back in with a tile vent, which is why originally looking to have it ducted out via a vent in the soffit to be able to angle it away.


  • Registered Users Posts: 272 ✭✭ electrofelix


    so 10mm by 1000 mm ( 1m length of eave) is 10,000mm2 and
    IIRC, the vented roof tiles are that size so one per meter, they need to be, both sides, along the bottom and some ups near the ridge, I forget the exact rules now :)

    I've just re-read this, and I think the front is about 5m so what you're saying is there would need to be 50,000mm2 of ventilation.

    Redoing the calculations with the soffit vents:
    max=(75/2)^2*pi*10=44170mm2
    min=(70/2)^2*pi*10=38480mm2

    Same for the back, since along the side there are only a couple of grills, it seems unlikely that there would be enough ventilation.

    Surely this is something that should have been sorted at installation time by stating that roof tiles would be required no matter what? or if they had install additional soffit vents along the side of the attic (hip roof) would that have sufficed, assuming that they installed the necessary ventilation baffles on all three sides?


  • Registered Users Posts: 10,928 ✭✭✭✭ Calahonda52


    The hip complicates it, the document is on the work computer and today is Sunday, or even Saturday :)

    I was not referring to the extractor fan, thats separate issue.

    IMO, while this is frowned upon here, ever regarded as heresy, is that if the attic is ventilated enough with tiles, a little moisture from a fan will not hang around

    ventilation baffles are rarely used in Ireland, "shurh why would you need them fancy yolks, we never needed them on the thatched roofs"

    my approach would be seal up the soffit vents and address it with roof tile vents
    this will reduce the risk of condensation on the ceiling at the wall ceiling connection, in the room below


  • Registered Users Posts: 272 ✭✭ electrofelix


    So I finally went and got some roof vent tiles fitted. Have ended up with some questions and possibly I should have done a smoke test beforehand to have a comparison.

    When I looked in the attic afterwards, there were no cuts through the felt for the roof tile vents? Called the contractor and they explained that given I had the bituminous underlay, that it would be risky to cut through it as it could end up tearing further than expected and that could result in leaks. They assured me that it's more common with the permeable membranes to see the cuts through, and what was there should be sufficient. If it wasn't, as the work was guaranteed for 10 years they could come back and add cuts but it would increase the risk of leaks.

    I would have thought given the bituminous felt would block so much that just having a tile vent over it would result in the air just flowing up the outside under the tiles but on the wrong side of the felt to provide ventilation to the attic itself? Or do you end up with sufficient air getting in under the overlapping felts to give enough circulation. Certainly seems like something that should be explained beforehand because I'm sure the common concept of such a vent is that it should provide direct ventilation to the attic space.

    My initial impression when I went up to the attic was that perhaps there is a slight breeze that I don't recall being there before, but whether that is my imagination?. Just the set up is sufficiently surprising and not being mentioned beforehand has me questioning whether it's really better.


    I also asked them to look at the extractor being hooked up to a proper exhaust either in the soffit or to one of the tile vents. They've indicated that when it was looked at it's going right out into the soffit to one of the existing soffit vents and there is no need to do anything about it. Use of the extractor around a shower coincided with humidity in the area of the attic near where the extractor ducting exits to the soffit going from 12.3C 82% -> 12.7C 86% -> 11.4C 84%. So anecdotally there is still leakage, but whether that is back from the soffit into the attic or from the existing ducting not sealing properly, not sure. I guess at least it's not hanging around?

    Is there any simple smoke creating tester that I could use in the bathroom with the extractor on to see what's happening rather than worrying or having to go up every couple of days and check for condensation? Possibly I should have thought to test this beforehand so I'd have a good comparison



  • Registered Users Posts: 3,144 ✭✭✭ 10-10-20


    So they ventilated the underside of the roof-tiles and didn't carry the vent though the non-breathable bitumen felt? Did they ride off on a horse afterwards?

    I perceive that smoke was being blown alright, but not in or around your attic. ;)

    "The best place to install tile or slate vents is just above your loft insulation, as the air here is able to draw out most of the moisture from the insulation without allowing heat to escape. To ensure that the placement of your vents is correct, you can poke a wire through your undersarking from inside your roof space to act as a marker. Once your marker is in place, simply cut an appropriately-sized hole in your undersarking where the rear of the vent will be laid and replace an existing roof tile with the vent."

    Let's see what the other more qualified boards.ie members think.



  • Registered Users Posts: 272 ✭✭ electrofelix


    The link certainly describes what I was expecting and had read, though I don't have the required knowledge/experience to counter the explanation put forward by the tradesman as being valid.

    I haven't paid yet so it would have to be a virtual horse for the moment.



  • Registered Users Posts: 3,144 ✭✭✭ 10-10-20


    If you can find the brand of the tile- there don't seem to be too many manufacturers anyway, see if they supply an installation guide online or ping them an email.



  • Registered Users Posts: 272 ✭✭ electrofelix


    Unfortunately that's unlikely to be possible as it would require going up on the roof to check. There wasn't any documentation for the tile vents left with me after the install.



  • Registered Users Posts: 272 ✭✭ electrofelix


    Happened to know someone that had a roofer as a relation, who unfortunately wasn't available to do the work, but has been able to answer some questions and confirm that there is no case where ventilation tiles would be fitted in this manner.



  • Registered Users Posts: 272 ✭✭ electrofelix


    Also discovered that the contractor was supposed to use scaffolding as this is a two story house, I guess had I known to ask about whether scaffolding would be used or not, it would be a quick way to filter out those that aren't genuine.



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  • Registered Users Posts: 4,954 ✭✭✭ zg3409


    Water on inside of felt in attic areas is common and normal in many cases. Warm air hitting cold felt causes it. Its like having condensation on inside of double glazing.


    Not to say you don't have an issue, but what is the problem causing? Storing stuff in attic eves it gets damp as it's not indoors anymore. Lights in attic areas need to be waterproof due to damp.



  • Registered Users Posts: 272 ✭✭ electrofelix


    It looked excessive rather than a small amount, as in the items on the attic floor had signs of plenty of drops falling directly on them not just being a little damp. As well as starting signs of mould and some of the rafters appearing damp. At the time it took about a week with a dessicant dehumidier to dry it out.

    When I go up there, the air feels dead as well. I'm not expecting wind, but certainly more of a draft when I open the attic when it's a bit breezy outside.

    I do have humidity/temp sensors placed at three points around the attic. The attic is about 5x8m, and the sensors are spread in a triangle to cover front, side and rear sections of the roof. I'm expecting that except when the sun is out shinning on the back roof, that I shouldn't be seeing sizeable differences in temp and humidity across the 3 sensors. However when the weather changes, I frequently see greater than 5 percentage points between front and rear sensor suggesting that as the humidity outside changes, there isn't enough of a flow of air across the attic to even it out within a reasonable amount of time. Thinking 1-2 hours should be enough to even it out rather than 6+.

    The sensors pick up when a shower is happening so there is a strong possibility that the extractor ducting was contributing as well as the insulation blocking the flow of air.



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