Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorthebeacon
    • CommentTimeJun 2nd 2019 edited
     
    Hello,

    I have purchased a 3-bed late Victorian terrace house in the UK, its about 130 years old. The house has a suspended wooden floor on joists and I plan to take up the floor and insulate between the joists.

    I have read a lot, including very helpful advice from Historic England (https://historicengland.org.uk/advice/technical-advice/energy-efficiency-and-historic-buildings/insulating-floors-in-historic-buildings/) regarding how best to renovate Victorian buildings.

    Upon taking up the floors we will inspect the state of the joists, electrics, plumbing, install more airbricks and treat all the wood work for wood worm/ beetles before installing the insulation.

    With regard to the planned renovating works I would like to get some advice on my proposed layout and have a few questions regarding logistics. We plan to lay (see attached image):


    1. Top layer: either solid or engineered tongue and groove oak floorboards.
    2. Below the floor boards: 18mm Plywood tongue and groove or OBS sheets
    3. Below the ply/ above the joists: Tyvek AirGuard Smart Air and Vapour Control Layer by Dupont (VCL) sealed to walls behind skirting.
    4. Between Joists: 150mm Breathable Thermafleece Cosy Wool Rolls Sheep's Wool Insulation
    5. Pro clima SOLITEX PLUS vapour permeable membrane. The membrane is draped up and over the joists to create a cradle to support the insulation material and its integral reinforced netting ensures it provides sufficient strength.


    I’m not intending on making a floating floor. One of the big questions I have is should I nail the plywood boards to the joists, which would mean nailing through he VCL? I can’t find anything online that suggests against it. The VCL is not a vapor barrier, its breathable. I could lay Tyvek Butyl Tape on top of the VCL running along all the joists, so when I nail through into the joists the tape will self seal the VCL. I would then secret nail the floor boards to the ply layer.

    With regard to the thickness of insulation required: the current requirement for a suspended floor is 0.22 - the calculation for my property comes in at 0.18 so well within that figure. Its suggested I use 150mm thick Cosywool as most applications look to exceed the 0.22 Requirement.

    Although I haven’t looked under the floorboards yet, what happens is the joists are not 150mm deep? Can I still install 150mm of insulation?


    Image credit: Ecological Building Shop.

    Thanks for your time.
      upgrading-suspended-floors-image.jpg
    • CommentAuthorjms452
    • CommentTimeJun 2nd 2019
     
    useful link:
    http://www.superhomes.org.uk/resources/insulate-a-floor/

    I'd suggest having a look under the floor before you get too far down the planning route. Old houses have a way of messing up the best laid plans.

    Personal preference but I like the idea of glass or rock wool insulation under a suspended floor in case of vermin, fire, leaks etc.).

    We attempted to future proof it and put 50mm drytherm 32 batts on chicken wire under 200mm joists with 200mm reused glass wool between (because we had bags of it for other parts of the renovation).

    You may also want to insulate down the walls a bit under the floor but this depends somewhat on where your wall insulation is.
    •  
      CommentAuthordjh
    • CommentTimeJun 2nd 2019
     
    Hello Tom, and welcome to the forum.

    I agree with John's comment about getting a look underneath as soon as possible and definitely before starting work. I also agree that inorganic wool insulation would be one less concern, although obviously they don't buffer humidity either. Depending on what the conditions near the walls are like it might be possible to combine inorganic wool in the centre area with sheeps wool near the walls.

    Also, unless there's clear evidence that the place has been rewired recently, I'd plan on replacing and probably upgrading all the wiring anyway. It will be much easier to do with the floor up than at any other time. The same goes for the plumbing but it is more conceivable that it will still have a long potential life. Equally, it's an even bigger job to replace at any other time, so spending some time and money now might be a very good investment. Note that in both cases, what you find might terrify you so much you won't want to use the existing cables/pipes until they are replaced, although hopefully it won't be that bad. You may also need to rewire to avoid the cables being surrounded by insulation.

    How much space is there underneath the joists? (another good reason to have a look before going much further). I take it there's no cellar. The space will make a difference to the possibilities and the ease of doing the job.

    If the joists aren't deep enough, it's quite normal to add battens underneath them to make them deeper, either parallel to the existing joists or at right angles which eliminates the thermal bridge. Or just suspend deeper insulation in pockets of membrane or mesh.

    Posted By: thebeaconOne of the big questions I have is should I nail the plywood boards to the joists, which would mean nailing through he VCL? I can’t find anything online that suggests against it.

    The Tyvek docs state: "Penetrations through the membrane should be kept to a minimum and any that are made should be sealed. All membrane laps should be sealed with Tyvek Acrylic Tape, and penetrations for pipework, wiring and electrical sockets should be made good with Tyvek FlexWrap." So I think it's clear nail holes should be sealed. The butyl tape would be a good choice as you suggest, IMHO.

    Having said that, some people don't like membranes at the top of floor insulation. It might be possible to use the membrane underneath your insulation as the airtightness barrier, or the T&G plywood subfloor.

    Engineered oak is more stable. It can be fitted as a floating floor or glued down as alternatives to secret nailing.
  1.  
    Hi Tom, I'm wondering about the following points...I'm deliberately not giving an answer, as every case needs to be considered and inspected rather than applying a "one size fits all".

    - you plan to use sheeps wool insulation, which can allow vapour passage, uptake, release. So why are you then planning to use a VCL, to control the amount of vapour passage, allowing for the plan to improve the air circulation with more air bricks?.

    - the vapour/moisture from inside the house has passed through the floor and away (presumably if the void is ventilated) prior to your purchase. How is that vapour now going to be released in the future once you seal the floor to a much greater extent? Condensation increase at other now relatively colder spots around the house (wall corners, windows)?

    - if the VCL is only controlling the rate (checking) the vapour flow, ie. allowing some vapour through, are a few nail holes really going to alter the desired effect? You've said you're not applying it as a vapour barrier.

    - if you do have more than the minimum 150mm depth below the joists (for air passage) I would recommend you let the breather membrane barrier sag below the joists, and fill with say 2 layers of 150mm insulation, so the insul goes right under the joist and meets it's saggy neighbour, keeping the joist bottom edge warm (much more important than vapour control in this case), and giving much better thermal performance. Watch where the air bricks are positioned, so they aren't covered, in which case add the plastic periscopes to bring the air below the sagging insulation.

    - you could lay a solid timber floor onto the joists, and forego the chipboard. That one depends upon who's installing the floor (saving on labour costs, but you'd need a secret nail applicator) and of course the cost/m2 of solid versus engineered. Buy it untreated, and brush on the Osmo oil yourself?

    Always more to think about than meets the eye..
    • CommentAuthorthebeacon
    • CommentTimeJun 9th 2019 edited
     
    .
    • CommentAuthorthebeacon
    • CommentTimeJun 9th 2019
     
    Thanks for the replies.

    Posted By: jms452
    I'd suggest having a look under the floor before you get too far down the planning route. Old houses have a way of messing up the best laid plans.


    That’s what I intend to do. Will be getting an electrician, plumber and damp surveyor in to inspect the condition under the floor before any materials are purchased or plans set in concrete.


    Posted By: djh
    I also agree that inorganic wool insulation would be one less concern, although obviously they don't buffer humidity either. Depending on what the conditions near the walls are like it might be possible to combine inorganic wool in the centre area with sheeps wool near the walls.


    The intention to use organic insulation is based on its hygroscopic properties. A number of the companies chemically treat the insulation to detract moths etc, is there still a rodent problem? Mineral wool is breathable, but doesn’t have the collecting and releasing properties sheep’s wool has. Would that be the next best option? Would it also be sensible to put a chicken wire or galvanised steel mesh under the joists to protect from the rodents?


    Posted By: djhYou may also need to rewire to avoid the cables being surrounded by insulation.


    This is something I have read about, I haven’t read up on how the electrics should pass through the insulation, I imagine this is something the electrician should know?


    Posted By: djh How much space is there underneath the joists? (another good reason to have a look before going much further). I take it there's no cellar. The space will make a difference to the possibilities and the ease of doing the job.


    I’m not sure I don’t have access yet. But hopefully in the coming weeks I will, when I can take up the floor boards. Then I will be in a better position on understanding the current situation and what work needs to be carried out.


    Posted By: djh Having said that, some people don't like membranes at the top of floor insulation. It might be possible to use the membrane underneath your insulation as the airtightness barrier, or the T&G plywood subfloor.


    Does the VCL not need to go on top of the joists to limit the warm air (which holds more water vapour than cold air) coming into contact with a material at a colder temperature, where the warm air meets a cold porous structural element the air may be cooled to such a point (especially as the floor cavity will be a lot colder than present) that the air becomes saturated (technically speaking it reaches its 'dewpoint', further cooling of the warm air then results in condensation forming? What’s the thought process/ reasoning for putting the VCL below?


    Posted By: GreenPaddy
    - you plan to use sheeps wool insulation, which can allow vapour passage, uptake, release. So why are you then planning to use a VCL, to control the amount of vapour passage, allowing for the plan to improve the air circulation with more air bricks?.


    The materials have the ability to ‘breathe’, allowing them to pass both air and moisture vapour controlled and slowly through, thus minimising and diffusing the danger of condensation. The surveyor has noted that there is currently inadequate air circulation in some parts of the floor and more air bricks would enable better circulation and removal of moisture as its released from building.


    Posted By: GreenPaddy
    - the vapour/moisture from inside the house has passed through the floor and away (presumably if the void is ventilated) prior to your purchase. How is that vapour now going to be released in the future once you seal the floor to a much greater extent? Condensation increase at other now relatively colder spots around the house (wall corners, windows)?


    The materials I’m proposing to use are all breathable. I don’t want to significantly reduce the permeability of the floor, but it will be reduced a bit. That said, the walls are going to be re-plastered with lime plaster, this should assist with limiting the build up of condensation and help control moisture levels inside.


    Posted By: GreenPaddy
    - you could lay a solid timber floor onto the joists, and forego the chipboard. That one depends upon who's installing the floor (saving on labour costs, but you'd need a secret nail applicator) and of course the cost/m2 of solid versus engineered. Buy it untreated, and brush on the Osmo oil yourself?.


    I’m planning on insulating the floor and laying the plywood floor myself ; I will get registered professionals in to carry out the electrics and plumbing, and will get a professional in to lay the floorboards. I will oil and seal the floor myself. Currently my budget is looking like it can stretch to a solid oak floor but engineered floor is a little too expensive. We are planning to get tongue and grooved solid oak boards to lay. We are thinking to install a plywood layer under the boards to enhance the thermal qualities (the ply is breathable though) and structural quality of the entire floor. Laying a ply layer would also allow for the option to not nail the floor if that’s a more suitable method…


    Thanks so much for everyone’s input so far
    • CommentAuthorMike1
    • CommentTimeJun 9th 2019 edited
     
    I'd agree with your basic proposal, other than the sheep's wool insulation, which has caused problems elsewhere. See this thread and the associated links for more: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15271 - my personal preference is for recycled plastic.

    If you choose engineered flooring, note that the top veneer comes in varying thickness, from 1mm up. The thinnest have a limited lifespan - they can't reliably be sanded without going through to the substrate (especially if they're not perfectly flat) - so I'd suggest going for 4 or 5mm at the least. Or solid boards.

    I've never yet come across a Victorian house that has sufficient under-floor ventilation to meet modern recommendations, so I too would recommend adding additional airbricks as per your surveyor's suggestion.

    The other option not mentioned above is the possibility of adding under-floor heating. Now would clearly be a good time to consider that as an option; it does have various benefits - improved comfort, the ability to use lower water temperatures compared to radiators, more wall space, etc.
    •  
      CommentAuthordjh
    • CommentTimeJun 9th 2019 edited
     
    Posted By: thebeaconThanks for the replies.
    Posted By: djh
    I also agree that inorganic wool insulation would be one less concern, although obviously they don't buffer humidity either. Depending on what the conditions near the walls are like it might be possible to combine inorganic wool in the centre area with sheeps wool near the walls.

    The intention to use organic insulation is based on its hygroscopic properties. A number of the companies chemically treat the insulation to detract moths etc, is there still a rodent problem? Mineral wool is breathable, but doesn’t have the collecting and releasing properties sheep’s wool has. Would that be the next best option? Would it also be sensible to put a chicken wire or galvanised steel mesh under the joists to protect from the rodents?

    You certainly need to keep moths out of wool, or kill any that do get in. And you certainly need to keep rodents or any other animals out - insulation makes attractive nesting material and/or sites. So if there's any way for small creatures to get into the under-floor space then yes I would put steel mesh of some kind. I'd think chicken wire has slightly too big a mesh size to keep small mice etc out.

    One question to answer is whether you actually need hygroscopic buffering there? What is its purpose?

    Posted By: djhYou may also need to rewire to avoid the cables being surrounded by insulation.

    This is something I have read about, I haven’t read up on how the electrics should pass through the insulation, I imagine this is something the electrician should know?

    Well, it's something they should know, but I wouldn't count on it. The current-carrying capacity of a cable has to be derated (i.e. reduced) where it is surrounded by insulation. So you must either run the cables outside the insulation or use a suitably larger cable size, which an electrician should be able to calculate. There's also the separate issue of polystyrene (EPS) causing the insulation of cables to self-destruct - put cables in conduits if required.

    Posted By: djhHaving said that, some people don't like membranes at the top of floor insulation. It might be possible to use the membrane underneath your insulation as the airtightness barrier, or the T&G plywood subfloor.

    Does the VCL not need to go on top of the joists to limit the warm air (which holds more water vapour than cold air) coming into contact with a material at a colder temperature, where the warm air meets a cold porous structural element the air may be cooled to such a point (especially as the floor cavity will be a lot colder than present) that the air becomes saturated (technically speaking it reaches its 'dewpoint', further cooling of the warm air then results in condensation forming? What’s the thought process/ reasoning for putting the VCL below?

    You need to distinguish between a VCL (VAPOUR control layer) and an AIRTIGHTNESS barrier. Inorganic insulation such as mineral wool doesn't much care about some condensation near the bottom, and it's more likely to form right at the bottom, on the surface or membrane.
    • CommentAuthorMike1
    • CommentTimeJun 9th 2019
     
    By the way, if you do choose T&G solid wood flooring, check the thickness of the timber above the tongue and groove; this limits the number of times it can be sanded (before the joints break / are exposed).

    It's possible that a better quality engineered board may allow more sanding than a cheap T&G solid board.
    • CommentAuthortony
    • CommentTimeJun 9th 2019
     
    ‘....wool doesn't much care about some condensation near the bottom, and it's more likely to form right at the bottom, on the surface or membrane.”

    I worry about organic insulation getting wet repeatedly and it will, having a breathable membrane underneath will allow vapour through but there will be water on top of it, this will soak into the wool and I think cause decay, smells and potentially fungal growth.

    I have removed mouldy mineral wool from a poorly ventilated loft with polythene sarking had it been wool I dread to think what it would have been like hygroscopic, breathable etc wouldn’t have helped.
    •  
      CommentAuthordjh
    • CommentTimeJun 10th 2019 edited
     
    Posted By: tony‘....wool doesn't much care about some condensation near the bottom

    I see you chose to misquote me. I specifically said 'Inorganic insulation such as mineral wool ...'.
    • CommentAuthortony
    • CommentTimeJun 10th 2019 edited
     
    Sorry trying to put the op off real wool
    • CommentAuthorthebeacon
    • CommentTimeJun 15th 2019 edited
     
    Thanks for all the advice, its really useful. We will get access to the property on the 28th, so will be able to assess the situation then.

    Posted By: djh<
    You need to distinguish between a VCL (VAPOUR control layer) and an AIRTIGHTNESS barrier. Inorganic insulation such as mineral wool doesn't much care about some condensation near the bottom, and it's more likely to form right at the bottom, on the surface or membrane.


    I think sheep’s wool is off the table now, and we intend to use mineral wool instead,

    I emailed Dupont enquiring about which membrane to install hanging over the joists and they suggest Tyvek® Supro breather membrane to hang over the joists and sit the insulation in. I’m still trying to get my head around the layers. In this use, would the Tyvek Supro be considered the Vapour Control Layer and air tightness barrier? Which means I won’t need to put an additional air tightness barrier under the joists, only a metal mesh.

    Is the metal mesh still required if im using mineral wool rather than sheeps wool?

    What would you suggest as the layer on top of the joists? Something like pro clima Intello Plus?

    Sorry if it feels like we are going round in circles, i’m just trying to understand each layers role.


    Posted By: Mike1
    If you choose engineered flooring, note that the top veneer comes in varying thickness, from 1mm up. The thinnest have a limited lifespan - they can't reliably be sanded without going through to the substrate (especially if they're not perfectly flat) - so I'd suggest going for 4 or 5mm at the least. Or solid boards.


    Posted By: Mike1By the way, if you do choose T&G solid wood flooring, check the thickness of the timber above the tongue and groove; this limits the number of times it can be sanded (before the joints break / are exposed).

    It's possible that a better quality engineered board may allow more sanding than a cheap T&G solid board.



    Thanks for the heads up. Not going to cut corners on the flooring quality.


    Is there anywhere i can be point to for further reading on best practice for cables running through insulation?


    Thanks again everyone!!!
    •  
      CommentAuthordjh
    • CommentTimeJun 15th 2019
     
    thebeacon asked: "Is there anywhere i can be point to for further reading on best practice for cables running through insulation?"

    https://www.voltimum.co.uk/articles/thermal-insulation-and-flat-twin-and
    • CommentAuthorjms452
    • CommentTimeJun 15th 2019
     
    Posted By: thebeaconIs the metal mesh still required if im using mineral wool rather than sheeps wool?


    If you've got a membrane under to 'wool' the only reason for metal would be to stop rodents and you'd have to go pretty fine to stop mice - so I suspect you don't need wire mesh.

    Posted By: thebeaconWhat would you suggest as the layer on top of the joists? Something like pro clima Intello Plus?

    We used this on top layer as air tightness but had no membrane underneath the insulation.

    The layer on the bottom needs to let through vapour more readily than the layer on the top. This stops you building up moisture in the insulation over time.
    • CommentAuthortony
    • CommentTimeJun 16th 2019
     
    I use strawberry netting under and combined vb/air tight layer on top (poly)
    •  
      CommentAuthordjh
    • CommentTimeJun 16th 2019
     
    Just a note for Tom, since he's new here.

    You're not going to get a consensus on this question, either here or anywhere else. We've been having discussions about it for 10 years or more. You'll find various websites that offer various solutions. Bear in mind that many are trying to sell products. What's best in your situation depends on the details of your situation, ranging from the physical details of the house, through to your own capabilities and emotional values.

    As long as you avoid things that you know to be clearly wrong, you probably won't go too far wrong. There's no way to know what the absolute best solution is for your situation.
    • CommentAuthorthebeacon
    • CommentTimeJul 1st 2019
     
    Hi all,

    i finally got into the house over the weekend and lifted some floor boards. I had an electrician come in and he will be redoing the the entire circuit.

    The floor joists are 90mm deep, at the front of the property there are two 75x230mm air bricks that have been blocked up. We plan to get these reopened and add an additional 1 so we will have 3. and at the rear we will add 2 more.

    The good news is we have 500mm of space between the joists and the ground.

    Currently the sleeper walls are solid. the only gap between the floor boards and the wall is between the 90mm joists.

    The current plan is to lay a floor like this:

    Solid or engineered oak T+G boards
    Pro Clima Intello VLC
    Insulation between the joists with a breathable insulation. Not Sheep wool due to animals and rotting, strongly considering rock wool now.
    layer hanging between the joists to sit the insulation in. (not sure what)
    Additional layer required under joists?

    To reach the recommended U value i will probably need 200mm of insulation. Is it a case of adding 130mm of baton to the joists or could i let the layer that is hanging over the joists simply hang lower?

    There will need to be air flow through the sleeper wall. I will take bricks out lower down the wall, below the level of insulation. Is there are suggestion on how often you should be removing a brick?

    The walls have been patched together over the years with various types of plaster. Installing the Pro Clima Intello VLC layer between the floor boards and insulation, i need to stick it to the walls to ensure its airtight. Should i remove the various plasters on the brickwork so the VCL attaches directly to the bricks?

    At the front of the property there has been rot, it didn’t feel that damp in there when i opened it up, but there has certainly been rot, to the point where the ends of the floor joists were rotting away. They will either need to be braced or replaced. In the past, someone had clearer removed what the joists were resting on and placed in a new piece of wood, then added small bits of wood to make the floor level. See the photos. this will need to be corrected.
      IMG_0043.jpg
    •  
      CommentAuthordjh
    • CommentTimeJul 1st 2019
     
    Posted By: thebeaconTo reach the recommended U value i will probably need 200mm of insulation. Is it a case of adding 130mm of baton to the joists or could i let the layer that is hanging over the joists simply hang lower?

    You can just let the material hang lower, so the loops either side of a joist are pushed together under the joist when filled with insulation.

    Posted By: thebeaconThe walls have been patched together over the years with various types of plaster. Installing the Pro Clima Intello VLC layer between the floor boards and insulation, i need to stick it to the walls to ensure its airtight. Should i remove the various plasters on the brickwork so the VCL attaches directly to the bricks?

    Brick or stone is normally not airtight, whereas plaster is (if in good condition). So it is usual to add at least a parge coat of plaster to a brick or stone wall before attaching a membrane (unless the membrane is of a type designed to be incorporated into the plaster when it is done).

    So I'd suggest looking at the plaster and deciding if it is sound or peeling or cracked. If it needs replacing or you want to replace it for aesthetic reasons then do that before (or whilst) attaching the membrane.

    With regards to the rot, you need to look at where the external ground level is and what material is adjacent to the wall, as well as where any damp proof materials are (engineering bricks or DPCs etc) to decide what the best way to protect the joists in future is.
  2.  
    If you're using rockwool between and under the joists, an option could be to fit wood wool boards bonded to rockwool and screw them into the bottom of the joist. We considered these for our ceilings, but just went with 25mm woodwool boards with rockwool between the joists.

    https://www.savolit.co.uk/products/savotherm
    • CommentAuthorjms452
    • CommentTimeJul 3rd 2019 edited
     
    Where the plaster was flakey we took it back to brick, rendered, primed and stuck the membrane to it. This all got plastered over later in the renovation.

    Membrane stuck to render is the first photo.

    There's lots of ways to get insulation under the joists. Our joists were 200mm so we only fitted 50mm drytherm slab underneath on netting (with long screws holding battens underneath the netting).

    Photo is from before slab went in
      IMG_1324.jpg
      IMG_1295.jpg
  3.  
    That looks good. How did you keep the netting taut? What kind of netting is that?
    • CommentAuthorjms452
    • CommentTimeJul 4th 2019
     
    It's scaffold netting - really strong & wide - also good for vegetables.
    https://www.scaffolding-direct.co.uk/debris-netting-3m-x-50m-green-.aspx

    Kept taught by being stapled to the battens at the ends and rolled round them a few times
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press