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BER after solar PV install unchanged - suggested upgrade wall insulation already done

  • 13-09-2022 11:06am
    Registered Users Posts: 273 ✭✭ electrofelix

    Recently got a 4kWp solar PV installation and I've checked the resulting BER that was published to discover that our B2 of 117.28kWh/m2/yr went to a B2 of 108.35kWh/m2/yr, which left me with some significant questions?

    Looking at the expected energy reduction per m2 due to the solar (6 panels west + 4 panels south at 30 degrees tilt, might be 35 but not 100% so went with the lower angle) I get the following calculation (allowing for some overshadowing for a low ball estimate):

    (0.8*(6*.4)*886*.8+0.8*(4*.4)*1074*.8) / 118m2 = 20.8

    AFAICT there is no overshadowing which would give the following:

    (0.8*(6*.4)*886*1+0.8*(4*.4)*1074*1) / 118m2 = 26.0664

    Instead I see less than 9kWh/m2/yr reduction. This seems a little low.

    Q1: am I doing the calculation above correctly?

    One Item that was flagged in the advisory report that seemed odd was the suggestion that the walls could be upgraded with insulation to get from a U value of 0.550 to a U value of 0.27.

    Note that when the assessor was here he did ask about the walls being insulated and I confirmed they were, but due to our young baby making a fuss and another contractor being here at the same time I couldn't put my hands on the documentation to go through it with him on the spot, which obviously would have likely avoided any issues by having the questions answered on the spot.

    Since we've already got the walls pumped with Korefill I looked up the cert and for 100mm cavity walls it's indicating that it should be already somewhere between 0.29 - 0.31. Now it's probably not as good as that in reality, but that seems to be quite a way off from 0.55.

    I did send a text to the assessor about whether the pumped walls were taken into account and they state that they were, but the above picture suggests to me that perhaps it's defaulting to the regulation cavity of 50mm which I believe is the minimum required, rather than the actual cavity. As I have an internal wall between a single story adjoining section and the two story part in which I happen to have a hole drilled to allow feeding through of a network cable I was able to confirm the block width is 100mm and determine the cavity depth as 100mm.

    I should be able to contact the previous contractor that installed the bead insulation to determine what they expected. Unfortunately the previous BER advisory didn't contain the same level of detail as to what various U values it was assuming for walls, windows, doors, etc, so there isn't anything to properly compare it against. Wanted to check whether what I'm thinking I'm reading makes sense before going around and chasing stuff down to bring up with the assessor.

    Q2: am I reading the table for the bead insulation correctly? Would 0.550 be the expected value for such walls?

    Q3: Do I need an explicit piece of documentation from the wall insulation installer on what the expected U value should be based on what they installed? Possibly I should have gotten something more at the time rather than an invoice detailing the amounts used and the general product cert.


  • Subscribers Posts: 37,767 ✭✭✭✭ sydthebeat

     Do I need an explicit piece of documentation from the wall insulation installer on what the expected U value should be based on what they installed? Possibly I should have gotten something more at the time rather than an invoice detailing the amounts used and the general product cert.

    you need explicit documentation from the installer, but not a u value calculation, bur that a "declaration of works" which would states they pumped "Xmm" thickness of cavity with "Y product", and it should also state of there was insulation in the cavity previously. if so, what type and thickness.

    the BER assessor is not allowed to take into account any insulations that cannot be seen measured and verified. therefore they require contractors documentary evidence when it comes to upgrades an renovations

    for new houses they actually require certifying engineers confirmation

  • Registered Users Posts: 273 ✭✭ electrofelix

    @sydthebeat thanks, that was exactly the problem, just wasn't clear from the response from the assessor what had happened. They had entered the U-Value for wall with standard insulation based on the year of construction.

    Once the correct documentation was dug out, it contained the details such as the existing insulation was 60mm EPS and remaining cavity was 50mm which was filled. They did note that the documentation should really include the manufacturer and model, now I do have an invoice containing the manufacturer, but the model is missing and I will need to follow up to ensure that I have something written from the installer.

    So mostly my own fault in not having the correct documentation to hand on the day the assessor called, a small bit due to the response from the assessor being confusing. If they had come back and said that the documentation for cavity pumped wasn't provided on the day and it was needed to enter anything else besides standard it probably would have been a bit quicker. But can't really expect them to remember specific house details where they have called a couple a weeks prior either.

    Anyway got it all sorted and the updated BER was a B1.

    Lesson learned, make sure you have all the documentation to hand, and I now have a digital copy of the installation docket along with the invoice put with any other BER details in a google drive to ensure it's all available.

  • Subscribers Posts: 37,767 ✭✭✭✭ sydthebeat

    good to hear you're sorted.

    this website if very useful but rarely used by BER assessors as notification to homeowners prior to an assessment