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.




Housing - Renovation: Filling under floor void - max depth?

Bottom of Page

1 to 28 of 28

  1.  
    • CommentAuthorWeeBeastie
    • CommentTimeJan 10th 2020
     
    Several threads with suggestions to fill underfloor voids completely with insulation (or backfill + insulation), thus creating a space which doesn't need to be vented.

    What's the max depth of void that would be sensible to fill?
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2020
     
    I don't think there is a maximum. I can't think why there would be.
    • CommentAuthorsam_cat
    • CommentTimeJan 10th 2020
     
    Cost is the only limit IMO.
    • CommentAuthorWeeBeastie
    • CommentTimeJan 10th 2020
     
    Is the outward pressure on external walls a factor??

    I'd like a giant version of squirty foam to fill the whole thing :bigsmile:
    • CommentAuthorphiledge
    • CommentTimeJan 10th 2020
     
    Id be more concerned about upward pressure on the underside of the floor than outward pressure on the walls. If you did do full filll foam it could be very messy to add or work on any services under the floor
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2020
     
    No, no, no! Underfloor voids are filled with loose-fill material, not foam.

    You can fill an infinite depth with hardcore. You can fill very large depths with EPS sheets or more expensively with EPS beads. You can fill complicated spaces with EPS beads.

    All are much, much cheaper than foam.
    • CommentAuthorWeeBeastie
    • CommentTimeJan 11th 2020
     
    Posted By: djhNo, no, no! Underfloor voids are filled with loose-fill material, not foam.

    You can fill an infinite depth with hardcore. You can fill very large depths with EPS sheets or more expensively with EPS beads. You can fill complicated spaces with EPS beads.

    All are much, much cheaper than foam.


    'Twas in jest!
    • CommentAuthorPetlyn
    • CommentTimeJan 13th 2020
     
    Or how about recycled glass beads: they are equally free-flowing, do not decay, are non compressible, proof against rodent/insect attack, fire proof and have a life measured in hundreds of years not tens of years.
  9.  
    I'm slightly bemused by this thread.

    I always thought that an adequately vented void below a suspended timber floor was absolutely vital to safeguard against damp induced rot.

    Has the received wisdom on this now changed and people are happily filling in the underfloor voids in their Victorian houses?
  10.  
    The thinking is that if the timbers are kept warm and dry then they won't rot. Blocking off the ventilation and not doing anything to keep the timbers warm is still going to be a problem and is to be discouraged.
  11.  
    <blockquote><cite>Posted By: Petlyn</cite>Or how about recycled glass beads: they are equally free-flowing, do not decay, are non compressible, proof against rodent/insect attack, fire proof and have a life measured in hundreds of years not tens of years.</blockquote>

    where does one get these cheaply?
  12.  
    Yes, but there in lies the problem - just exactly how does one go about categorically assuring that the timbers are kept warm and especially dry?

    What about, for example, the all too common rotting out of joist ends that are placed directly onto masonry that can wick moisture from the ground? It seems to me that blocking off all ventilation in this scenario is an absolute recipe for disaster - especially if the area is now warmer because of all the additional insulation provided by the newly installed fill.

    Granted, if you have this situation then your timbers are at risk anyway, but they must surely be placed in hugely greater jeopardy if you infill around them?

    I must confess that I have been contemplating insulating underneath an existing suspended timber floor but my thoughts are running along the lines of lifting the boards and insulating between the joists and around the periphery with PIR, leaving the underside of the joists open to the cross ventilation to help deal with any moisture issues, but clearly this is vastly (immensely!) more work than flood filling the void with beads of some sort.
    •  
      CommentAuthordjh
    • CommentTimeJan 14th 2020
     
    Posted By: ealingbadgerYes, but there in lies the problem - just exactly how does one go about categorically assuring that the timbers are kept warm and especially dry?

    Careful design by an experienced/qualified/competent/insured designer? And a suitable contract with said designer.
  14.  
    Posted By: ealingbadger
    Granted, if you have this situation then your timbers are at risk anyway, but they must surely be placed in hugely greater jeopardy if you infill around them?


    I don't really like suspended timber floors, especially those built into walls - if there is any sign of moisture or rot at joist ends then the lot should be replaced, ideally with a solid floor. If there is no sign of any deterioration I don't think that increasing the temperature of the floor joists by fully filling is likely to cause any damage. What you are suggesting I think would be more likely to cause problems than fully filling - you are going for a half way house and allowing the joists to stay cold by not covering the bottom of them. You can model the heat flow for your own situation and see, but the cost of paying someone suitably qualified to survey and model is likely to be more than the cost of replacing the floor! If it was reasonable fully fill then I would be tempted to do so but would also try and replace with a concrete floor and UFH pipes to enable the use of the thermal capacity of the slab.
  15.  
    Posted By: djh
    Posted By: ealingbadgerYes, but there in lies the problem - just exactly how does one go about categorically assuring that the timbers are kept warm and especially dry?

    Careful design by an experienced/qualified/competent/insured designer? And a suitable contract with said designer.


    You are an optimistic soul aren't you. :bigsmile:
  16.  
    Posted By: willie.macleod
    Posted By: ealingbadger
    Granted, if you have this situation then your timbers are at risk anyway, but they must surely be placed in hugely greater jeopardy if you infill around them?


    I don't really like suspended timber floors, especially those built into walls - if there is any sign of moisture or rot at joist ends then the lot should be replaced, ideally with a solid floor. If there is no sign of any deterioration I don't think that increasing the temperature of the floor joists by fully filling is likely to cause any damage. What you are suggesting I think would be more likely to cause problems than fully filling - you are going for a half way house and allowing the joists to stay cold by not covering the bottom of them. You can model the heat flow for your own situation and see, but the cost of paying someone suitably qualified to survey and model is likely to be more than the cost of replacing the floor! If it was reasonable fully fill then I would be tempted to do so but would also try and replace with a concrete floor and UFH pipes to enable the use of the thermal capacity of the slab.


    I think we are looking at things from completely different perspectives. My own is related to ensuring that any work that I undertake does not damage the fabric or patina of a Victorian era house where joists built into walls is the norm and the idea of replacing anything with concrete is complete anathema.

    I am not convinced that raising the temperature is sufficient. Mould growth is related to temperature and moisture and if raising the temperature with a permeable infill such as polystyrene or glass beads which at the same time is also likely to harbour and retain any accumulated / accumulating moisture rather than blasting it through and out with a sufficiently open path for a good breeze is a recipe for likely disaster IMV.

    Now I do not claim to be an expert but those that do constantly emphasise the importance of ventilation to prevent timber rot. I would be more than happy to be shown the error of my ways but until then...

    I am not averse to concrete in an appropriate setting BTW. My new workshop which I am building down the end of the garden has an engineered concrete slab snuggling in an external blanket of 300mm of XPS and is being built to Passivhaus standards.
    • CommentAuthorKenny_M
    • CommentTimeJan 15th 2020
     
    I find this idea of fully filling the void under old houses to be really interesting, and if it pans out its doesn't just help with insulating the floor, but also with all the draughts that are probably an even bigger problem in old houses.

    However, like ealingbadger, I'm not convinced that that keeping the joists warm will be enough, or that something like EPS bead is permeable enough to deal with any moisture build up. I think the thing that also might be getting missed here is where the moisture comes from in an old house and its often transferring from the ground through the walls into the joist ends and ventilation is needed to carry this away. There are also often at least one part of the house where the floor is solid, and if the ventilation can't reach that the dampness goes up the internal walls.

    Like back when people thought it would be a great idea to cover old houses with cement render or impermeable paint, it will be years later before we know whether this turned out to be a good idea or not.
  18.  
    Posted By: ealingbadger
    I think we are looking at things from completely different perspectives. My own is related to ensuring that any work that I undertake does not damage the fabric or patina of a Victorian era house where joists built into walls is the norm and the idea of replacing anything with concrete is complete anathema.

    I am not averse to concrete in an appropriate setting BTW. My new workshop which I am building down the end of the garden has an engineered concrete slab snuggling in an external blanket of 300mm of XPS and is being built to Passivhaus standards.

    Have you looked at using limecrete, rather than concrete? It's breathable and much more suited for older properties. We installed it into part of our home (a grade 2 listed former mill dating back to circa 1752) and have had zero problems with it. The floor build up consisted of a layer of coated leca with a mixture of lime and pummice stone on top, with a top layer lime screed holding UFH pipes. The floor is surfaced with flagstones. We've had zero damp issues in that area since the work was carried out about 9 years ago. The only change I'd make if I did it again would be to use recycled foam glass instead of the leca and pummice stone.

    I tend to agree with some of the others that fully filling a void in an old house with solid walls is asking for trouble, so if you don't want the hassle/expense of fitting a solid limecrete floor I'd just fit breathable insulation between the joists and be content with a warmer house that may not be as well insulated as a modern home, but is much better than a comparable un-insulated Victorian home.
  19.  
    The joist ends are always likely to be the biggest issue and are a fundamental problem with this type of building which no-one has easy answers to and there is no one size fits all. They will be the coldest part of the joist and attract moisture, but just how much and whether they remain in a risky state for a significant period of time depends on the individual joist. Proper DPCs and externally insulating the outside to help raise the temperature of the masonry may help address the issues and I understand folk wanting to keep a certain look/originality but that does come at a cost.

    I do like deep insulation followed by UFH embedded in a screed. The low temperature, high capacity heat storage is preferable to me rather than a drafty, cold, bouncy, slowly rotting floor! Having grown up in a Victorian era house, I can confirm that when the suspended floors were ripped out and replaced with insulated concrete slabs with UFH pipes 25 years ago it was one of the best upgrades for both user comfort and heating efficiency, also helping maintain the rest of the building fabric.
    • CommentAuthorMike1
    • CommentTimeJan 16th 2020
     
    <blockquote><cite>Posted By: ealingbadger</cite>I'm slightly bemused by this thread.

    I always thought that an adequately vented void below a suspended timber floor was absolutely vital to safeguard against damp induced rot.

    Has the received wisdom on this now changed and people are happily filling in the underfloor voids in their Victorian houses?</blockquote>

    Since it hasn't not been mentioned on this forum for a while, it's worth taking a look at the conclusions of research undertaken by Sofie Pelsmakers at http://www.sofiepelsmakers.com/suspended-timber-ground-floors.html

    I can see the reasoning behind filling a floor void, but I'd be very hesitant to do it myself. I've always opted to remove the timber floor and replace it with concrete on insulation...
  21.  
    We fully filled the floor voids of 50+ houses we renovated 10/15 years ago with EPS Bead and sealed up the vents including my own Victorian Red Brick, we've had no problems. I returned to one particular house every winter for a few years to check the moisture content of the joist at the middle of the floor and where it enters the wall, there was no difference in the moisture content of the joists. Joist ends become warmer than joist ends in an uninsulated floor void wall. The temperature difference between the internal wall between the joists and where the joist meets the wall is about 0.2 Degrees C.

    A few things to note:
    1. Insulating a wall and floor concentrates heat loss at the wall/floor junction increasing it's temperature.
    2. Insulating one side of a rising wall increases it's temperature and reduces capillary moisture pull up the wall.
    3. Insulating below the floor increased the temperature of the floor joists eliminating condensation risk.
    4. Closing the floor vents improves airtightness.

    I presented 4 PH Renovation projects at the UK PassiveHaus Conference in 2008 where I met Sofie Pelsmaker, she was intrigued and decided to do a research project on it. I removed the beads from a 1m x 1.5m section of my neighbours house after 5 years because he wanted to store wine. The walls and the soil beneath was bone dry.
    I flexed some of the cables to see if they were brittle but couldn't detect brittleness. I believe the PVA Glue surrounding the beads prevents plasticine leaching from the cables but can't be sure.
    Electric cables surrounded by insulation should be derated by putting a lower Amp breaker on that circuit.
      gr23b.jpg
  22.  
    Were you pumping in the beads straight onto an earth bed or did you put any kind of membrane down first?
  23.  
    Posted By: ealingbadgerWere you pumping in the beads straight onto an earth bed or did you put any kind of membrane down first?
    We pumped directly onto the earth.
    • CommentAuthorKenny_M
    • CommentTimeJan 28th 2020
     
    Posted By: Viking HouseWe fully filled the floor voids of 50+ houses we renovated 10/15 years ago with EPS Bead


    Did any of these houses have solid floors adjacent to the room being filled with EPS?

    This would be a quick and easy win for me in my two front rooms, but the hallway and the back of the house are solid, and my impression is that these would be less well ventilated if there was no air getting to their internal boundaries. Having said that, I suppose it is also possible that by blocking the air flow to them, and insulating that boundary, it might raise the temperature of the ground at those edges and reduce the dampness.
  25.  
    Posted By: Kenny_M
    We fully filled the floor voids of 50+ houses we renovated 10/15 years ago with EPS Bead



    Posted By: Kenny_MDid any of these houses have solid floors adjacent to the room being filled with EPS?


    Given that filling the floor void stops any ventilation having solid floors shouldn't make any difference.

    Ventilation under floor is required to remove condensation caused by parts being below dew point. Filled with insulation the area will be above dew point so no condensation.

    Also condensation will only form at a material/air junction. if there is no such junction then there will be no condensation.
    • CommentAuthorKenny_M
    • CommentTimeJan 29th 2020
     
    Posted By: Peter_in_HungaryGiven that filling the floor void stops any ventilation having solid floors shouldn't make any difference.

    Ventilation under floor is required to remove condensation caused by parts being below dew point. Filled with insulation the area will be above dew point so no condensation.

    Also condensation will only form at a material/air junction. if there is no such junction then there will be no condensation.


    So my thinking here is that damp rises up from the ground on a traditional, solid floor that pre-dates damp proof courses. In my case the solid hallway floor, is adjacent to two suspended timber floor rooms. The ventilation to the under floor of these rooms will also presumably help to carry away moisture from the edges of the solid floor. If I take away that ventilation, will the dampness instead be forced up and out at the base of the wall?

    Likewise, the internal walls also carry damp up from the ground, and should hopefully be dispersed by the ventilation. If there is no ventilation would this not also tend to continue upwards and out around the skirting board area?

    Is it possible that the properties where this was done while old, were new enough to have a dpc? Would it make a difference to the theory behind this if there were no dpc?
  27.  
    Posted By: Kenny_MIs it possible that the properties where this was done while old, were new enough to have a dpc? Would it make a difference to the theory behind this if there were no dpc?
    Both my house and my neighbours house were built in 1880 without dpcs.
    • CommentAuthorKenny_M
    • CommentTimeFeb 5th 2020
     
    Posted By: Viking HouseBoth my house and my neighbours house were built in 1880 without dpcs.


    That's really interesting, thanks for the response.

    I get damp at the base of the walls of my solid hallway, and on the back wall of a front room where it meets a higher, solid floor part of the house. I had long thought that what I need to do is fix the under floor ventilation to reach these walls, but maybe insulating and keeping these junctions warmer would be a more effective alternative. Food for thought.

1 to 28 of 28

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press