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General: Loft Insulation Cost Comparison

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  1.  
    Easy enough to make your own loft legs from timber, cross braced to prevent racking.
    The problem with board insulation is 1)cost and 2) getting a good seal between the boards. Will all the ducting be above the insulation, I suspect that the return should be under the insulation and the intake above, if so can't you put the under insulation ducting in now and avoid the problem of disturbing the insulation?
    •  
      CommentAuthordjh
    • CommentTimeJan 11th 2016 edited
     
    Posted By: VictorianecoYeah just googled, 175mm depth. Would PIR insulation be okay to walk on? Killing two birds with one stone

    Yes, but might also kill your wallet. Rigid insulation sold for use in the loft is usually XPS in my experience.

    Silly question but if I insulate the attic space with say 400mm wool, and I need to walk in the attic at some point to install the ducting for my MVHR system, what is the best method of doing so without falling through the ceiling?

    You want the ducting within the heated envelope. i.e. underneath the insulation. So best to install the ducting first.

    Edit: Supply and extract inside the heated envelope. Intake and exhaust outside the heated envelope but still insulated is ideal. The MVHR unit should be inside the thermal envelope as well if possible.
  3.  
    Posted By: djhYou want the ducting within the heated envelope. i.e. underneath the insulation. So best to install the ducting first.

    I thought the input flow (cold) went outside the insulation and the return (warm) went inside the insulation. Otherwise the cold inflow would be warmed up taking heat from the house and the heat exchanger in the MVHR would have little to do and the warm air return would be exhausted warmer because of a warmer input side ( the closer in temperature the exhaust and input are the less heat will be transferred).
    • CommentAuthorcjard
    • CommentTimeJan 11th 2016 edited
     
    MVHR dicts should be arranged so the connection to the world is as short as possible. Insulate both the pipes that connect the MVHR to the world. This is intended to prevent condensation for in on the outside of the incoming pipe and the inside of the outgoing pipe. Have all the duct runs between rooms and MVHR within the thermal envelope of the house. This means they need no insulating. The air that they're carrying is as warm as the house air, essentially so if they run through a cold space they will cool. This is either your warmed fresh air that is cooling, or its your heat laden stale air. Loss of heat from either represents a loss of heat from the warm envelope.

    Summary
    Between room and MVHR you care about losing the valuable heat
    Between the MVHR and world you care about the nuisance condensation

    Being insulated or in a warm envelope addresses both problems
  5.  
    Good advice succinctly put cjard.
  6.  
    Not sure PIR would break the bank for 14m2 of attic space compared to 400mm of loft insulation. I guess I'll try and route the mvhr pipes first but not sure they'll be able to be within the envelope due to where they go.
    •  
      CommentAuthordjh
    • CommentTimeJan 12th 2016
     
    Posted By: Victorianeconot sure they'll be able to be within the envelope

    If they're not then they need really good insulation - even the standard insulated ducting is not enough I've been told. There's no point having an MVHR if you then lose all the HR through the ducts!
    • CommentAuthorringi
    • CommentTimeJan 12th 2016
     
    The envelope can be expanded cheaply by using lots of loft insulation (mineral wool type) over and beside the ducts. Just pile up lots of insulation and it will cover the ducts running over the ceiling joist.
    • CommentAuthorShevek
    • CommentTimeJan 13th 2016 edited
     
    Hope you don't mind cjard, I swiped your nice ductwork design description and added it to the Designing Buildings wiki:
    http://www.designingbuildings.co.uk/wiki/Mechanical_ventilation_with_heat_recovery_MVHR
    •  
      CommentAuthordjh
    • CommentTimeJan 13th 2016
     
    Posted By: ShevekHope you don't mind cjard, I swiped your nice ductwork design description and added it to the Designing Buildings wiki:
    http://www.designingbuildings.co.uk/wiki/Mechanical_ventilation_with_heat_recovery_MVHR

    Hmm, so if it's permanently published then perhaps we should care more about its accuracy. Condensation on both the intake and exhaust ducts is likely to be on the outside, unless the exhaust duct is run through a space where the air is cooler than that in the duct, which is unlikely.

    Note that if the system has a post heater then the supply distribution ducts need some insulation as well.
    • CommentAuthorShevek
    • CommentTimeJan 14th 2016
     
    • CommentAuthorconverse
    • CommentTimeJan 14th 2016
     
    With loft insulation I have found that it is cheaper to pay an insulation company to install it than to install it ourselves, so get a quote from specialist as well as just looking at material cost. They buy the stuff in huge quantities so get much better prices than occasional users.
    • CommentAuthorjamesingram
    • CommentTimeJan 14th 2016 edited
     
    VE 15m2 will be about 11 sheets to get 200mm PUR=400mm quilt so £330-50 ish
    quilt will be about £100
    I usually stick a few bits of 3-4/2 from rafter to central wall plate up around 400mm and stick some
    t&G on that for light storage
  14.  
    like your wiki shevek do you have a thread here on it ?
    •  
      CommentAuthordjh
    • CommentTimeJan 14th 2016
     
    Posted By: converseWith loft insulation I have found that it is cheaper to pay an insulation company to install it than to install it ourselves, so get a quote from specialist as well as just looking at material cost. They buy the stuff in huge quantities so get much better prices than occasional users.

    Am I right in thinking that if you get an installer to supply and install it's charged at 5% VAT whilst if you buy your own it's 20%? Though I also seem to remember the EU are going to force us to change that.
    • CommentAuthorcjard
    • CommentTimeJan 14th 2016 edited
     
    Posted By: djhCondensation on both the intake and exhaust ducts is likely to be on the outside, unless the exhaust duct is run through a space where the air is cooler than that in the duct, which is unlikely.


    Condensation is going to be on whichever surface the warmer air is touching. I thought we were discussing running ducts through a cold loft space in this particular context, though I do believe you're right in that it's perhaps more usual to encounter the s/e ducts in the warm envelope
    • CommentAuthorShevek
    • CommentTimeJan 14th 2016
     
    <blockquote><cite>Posted By: jamesingram</cite>like your wiki shevek do you have a thread here on it ?</blockquote>
    I wish I could take credit for that Wiki. You can read about it here:
    http://www.designingbuildings.co.uk/wiki/User:Designing_Buildings

    I'll post a thread to introduce it to everybody.
    •  
      CommentAuthordjh
    • CommentTimeJan 14th 2016
     
    Posted By: cjard
    Posted By: djhCondensation on both the intake and exhaust ducts is likely to be on the outside, unless the exhaust duct is run through a space where the air is cooler than that in the duct, which is unlikely.

    Condensation is going to be on whichever surface the warmer air is touching. I thought we were discussing running ducts through a cold loft space in this particular context, though I do believe you're right in that it's perhaps more usual to encounter the s/e ducts in the warm envelope

    Exactly and both the intake and exhaust ducts contain air at nearly external air temperature. The intake because it contains outside air that is being 'sucked' into the MVHR and the exhaust because it contains air that has been cooled to nearly the outside air temperature by the MVHR unit. The loft contains air at somewhere between the outside temperature and the inside temperature, depending on insulation and airtightness etc.

    Condensation inside the pipes, should it occur, is not generally a nuisance since they're angled down in order to deal with wind-driven rain etc.
  19.  
    Knauf earthwool 100mm
    # U-value 0.044
    # R-Value 2.25
    # Roll Area 13.89m²
    # £15.49 Robert Price

    £0.50 per 1m² of 1 R-value
    • CommentAuthortony
    • CommentTimeJul 8th 2016
     
    Go for it
    • CommentAuthorEd Davies
    • CommentTimeJul 8th 2016
     
    Posted By: Victorianeco# U-value 0.044
    That'll be conductivity (λ or κ), not U-value. If anybody can get a U-value of 0.044 W/(m²·K) with 100 mm of material at those sorts of prices we can just shut this forum down.

    The U-value is the conductivity divided by the thickness: 0.044 W/(m·K) / 0.1 m = 0.44 W/(m²·K).
  22.  
    Ed, I suspect that may be Knauf's mistake rather than VE's. I can't remember the manuf, but I bought a roll recently where what should have been Lambda was labelled as 'U Value'.
    • CommentAuthorcjard
    • CommentTimeJul 8th 2016
     
    <blockquote><cite>Posted By: Victorianeco</cite>Knauf earthwool 100mm
    # U-value 0.044
    # R-Value 2.25
    # Roll Area 13.89m²
    # £15.49 Robert Price

    £0.50 per 1m² of 1 R-value</blockquote>

    http://www.secondsandco.co.uk/#!product-page/c1n8h/48d91ab7-cb94-33d1-2367-5353c803dbdb

    100mm roll, 10 sqm, ten quid..
    • CommentAuthorEd Davies
    • CommentTimeJul 8th 2016
     
    Yep, seen similar on rolls in one of the DIY sheds.
    • CommentAuthorFlubba
    • CommentTimeJul 9th 2016
     
    I take it the days of the £3 roll of Knauf in whatever thickness you like are long gone?
    • CommentAuthortony
    • CommentTimeJul 9th 2016
     
    Yes, subsidised and long gone
    • CommentAuthorgravelld
    • CommentTimeJul 9th 2016
     
    Keep your eye on local Facebook groups, got some for £3 last summer.
  28.  
    <blockquote><cite>Posted By: cjard</cite><blockquote><cite>Posted By: Victorianeco</cite>Knauf earthwool 100mm
    # U-value 0.044
    # R-Value 2.25
    # Roll Area 13.89m²
    # £15.49 Robert Price

    £0.50 per 1m² of 1 R-value</blockquote>

    <a href="http://www.secondsandco.co.uk/#!product-page/c1n8h/48d91ab7-cb94-33d1-2367-5353c803dbdb" rel="nofollow">http://www.secondsandco.co.uk/#!product-page/c1n8h/48d91ab7-cb94-33d1-2367-5353c803dbdb</a>

    100mm roll, 10 sqm, ten quid..</blockquote>

    When I rang these and they wanted £45 delivery per order so the cost per roll actually went up for what I would need.

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