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Housing - Renovation: Underfloor insulation - kingspan beneath or between joists?

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  1.  
    Once again, on the subject of my timber bungalow.

    I'm about to insulate a few floors via the crawl space. There's just about enough room for me to wiggle along the bays between the sleeper walls. I've tried in the past somewhat unsuccessfully to fill the space between the joists with glass wool, but there's just not the room to manoeuvre whilst covering over with netting or membrane.

    Having experimented, it's going to be much easier to fit rigid board. Given the joists are only 3", and I have a number of 50mm kingspan sheets laying around, I could fit them between joists. I've also considered the more preferable solution of fitting to the underside of the joists - less cuts, keeps the joists warm etc, but due to the aforementioned lack of manoeuvrability along with the 4x2 purlins restricting insulation board placement tight up against them, I'd have to use thinner boards. I've again experimented with an off-cut of 25mm, and this fits the bill.

    Can more knowledgable members suggest how I should detail either solution for a rot-free subfloor? In particular I'm wondering what I do about the purlins - do I butt the boards up to them? Naturally this will leave an insulated void between floorboard and purlin. Around the perimeter the studwork walls sit on the joists shared by the floor, so do I stick insulation board right underneath, touching the exterior cladding? I wonder how air-tight I could feasibly make such a junction given the limited wriggle room, but I could certainly pre-foam said difficult areas before sliding the insulating boards in.

    As always, any help would be much appreciated :wink:
    • CommentAuthorgyrogear
    • CommentTimeApr 11th 2017 edited
     
    Neither - just glue the insulation to the perimeter walls.

    You will use less insulation, and more efficiently.

    gg
    •  
      CommentAuthordjh
    • CommentTimeApr 11th 2017
     
    I'd be tempted to look at Tom's solution for filling the crawlspace with some blown-in or tipped in insulation.
  4.  
    Posted By: gyrogearNeither - just glue the insulation to the perimeter walls.

    You will use less insulation, and more efficiently.

    gg


    Wouldn't this mean blocking up the subfloor vents, and thus risking the structure?

    Posted By: djhI'd be tempted to look at Tom's solution for filling the crawlspace with some blown-in or tipped in insulation.


    Yes, I've looked at that. Probably the best way forward, but the issue I have is that I'm renovating in stages. I guess I could leave the subfloors completely uninsulated until such time that I'm ready to proceed, but I'd still need access. I also haven't a clue where to start in terms of finding someone who could and would be prepared to do it.
    • CommentAuthorgyrogear
    • CommentTimeApr 12th 2017 edited
     
    Posted By: alexoftheorchardWouldn't this mean blocking up the subfloor vents, and thus risking the structure?


    Yes and No.

    Yes because you block up all of the vents except one.

    No because blocking the vents should not "risk the structure" any more than having said vents open.

    The idea is to lost-ventilate the subfloor using house air: continuously operated mechanical exhaust ventilation, at around 1 CFM per 50 square foot of area.

    Now the structure gets ventilated with conditioned air, rather than washed with cold air in winter and warm moist air in summer.

    gg
  6.  
    Posted By: gyrogear
    Posted By: alexoftheorchardWouldn't this mean blocking up the subfloor vents, and thus risking the structure?


    Yes and No.

    Yes because you block up all of the vents except one.

    No because blocking the vents does not "risk the structure" any more than having said vents open.

    The idea is to lost-ventilate the subfloor using house air: continuously operated mechanical exhaust ventilation, at around 1 CFM per 50 square foot of area.

    Now the structure gets ventilated with conditioned air, rather than washed with cold air in winter and warm moist air in summer.

    gg


    That sounds like a lot of faff for little return. Do you have any more details? Surely this would mean more heat lost rather than trapped if I'm using house air to warm the subfloor?
    • CommentAuthorgyrogear
    • CommentTimeApr 12th 2017
     
    I actually did not suggest warming the subfloor, but ventilating it.

    (A perimeter-insulated sub-floor void does, in fact, become a de facto heated volume by dint of resistance to inward-flowing coolth from outside, but that is an ancillary (though useful) issue here).

    Plenty of sources on the web - here is one, for example:

    http://www.energyvanguard.com/blog/70974/What-Is-the-Best-Way-to-Deal-with-Crawl-Space-Air

    gg
  8.  
    That article discusses US crawl spaces though, and I'd imagine the climate is wildly different from that of North East England.

    My primary question here is how I can insulate it without causing problems. I like the idea of perimeter insulation vs under floorboard / joist insulation, but adding ductwork down there and a supply from an MVHR does seem somewhat unorthodox. Is it actually going to benefit the property vs just leaving it as it's been since 1940 (well ventilated, uninsulated, trouble free)?
    • CommentAuthorgyrogear
    • CommentTimeApr 12th 2017
     
    Posted By: alexoftheorchardbut adding ductwork down there and a supply from an MVHR


    How do you get to here ?

    gg
  10.  
    Posted By: gyrogear
    Posted By: alexoftheorchardbut adding ductwork down there and a supply from an MVHR


    How do you get to here ?

    gg


    Perhaps an assumption, but the article you linked talked about bringing a duct from the house ventilation system down to the crawl space. Do you mean a simple fan blowing out the one remaining open vent, putting the crawl space under negative pressure? Would this mean opening a vent in the floor to introduce house air, or simply omitting that part?

    Would such a configuration, along with perimeter insulation, provide a noticeable improvement on the current situation? Is there anything else involved?
    • CommentAuthorgyrogear
    • CommentTimeApr 12th 2017 edited
     
    Yes, a penetration in the main floor somewhere surreptitious, with a small DC fan (such as PC case fan) shoving air downwards; or like you say, on the vent, pulling the air through the crawl (although pushing produces a more turbulent flow...).

    Depending on the area in question (my smallest PC case fan pulls 19 cfm).

    Regarding the improvement, you would have to test it I expect.

    What else is there involved ?
    Well, depends on the state of your underfloor: any damp, or mould for example ?
    If earth floor, you could treat it with lime (NHL) to discourage bacterial growth.
    Although from what you say, it sounds pretty benign...


    Posted By: alexoftheorchardIs it actually going to benefit the property vs just leaving it as it's been since 1940 (well ventilated, uninsulated, trouble free)?


    Old RAF adage: "(if it moves, salute it; if it don't, paint it; and) if it's not broke, don't repair it..." :cool:

    gg
  12.  
    Posted By: gyrogearYes, a penetration in the main floor somewhere surreptitious, with a small DC fan (such as PC case fan) shoving air downwards; or like you say, on the vent, pulling the air through the crawl (although pushing produces a more turbulent flow...).

    Depending on the area in question (my smallest PC case fan pulls 19 cfm).

    Regarding the improvement, you would have to test it I expect.

    What else is there involved ?
    Well, depends on the state of your underfloor: any damp, or mould for example ?
    If earth floor, you could treat it with lime (NHL) to discourage bacterial growth.
    Although from what you say, it sounds pretty benign...


    Posted By: alexoftheorchardIs it actually going to benefit the property vs just leaving it as it's been since 1940 (well ventilated, uninsulated, trouble free)?


    Old RAF adage: "(if it moves, salute it; if it don't, paint it; and) if it's not broke, don't repair it..."https:///newforum/extensions/Vanillacons/smilies/standard/cool.gif" alt=":cool:" title=":cool:" >

    gg


    Ha, well what's 'broken' is my bank account, and the other half is always cold. I suspect we're losing a lot of heat down to the subfloor given how well it's ventilated and our exposed and windy location halfway up a hill.

    Sounds like an interesting solution. Have you tested such a setup yourself? I looked at Tom's solution of 'cofferdam' insulation going below the subfloor around the outer perimeter and blocking the vents (I replied to an old thread referring to this earlier). If that's proved to work, I might be able to do something similar, with the only restriction being the depth of insulation I can get without going all out and digging up the concrete paths around the house.
    • CommentAuthorgyrogear
    • CommentTimeApr 13th 2017
     
    Posted By: alexoftheorchardHave you tested such a setup yourself?


    Yes, I insulated the walls (16 sq.m versus 42 square meters of soffit) and blocked up one grille in the process and the second grille I use for blowing warm basement air in, (but somewhat more than the recommendation) ; the exhaust air is blown through the cellar and out of a small window. At the moment it is unducted, but this will be remedied "shortly"...

    The fan runs off a timer during the day, pulling heat into the CS, which I get back at night.
    Since running this system, CS temperature has increased by around 3.5°C on average.

    gg
  14.  
    Interesting. Is there a noticeable difference to floor temps? Measurable drop in heating demand?

    I'll have to work out how best to detail perimeter insulation around the purlin / bearer ends and the underside of the external walls (they're supported every 1.5 metres, the bottom of the wall 2" clear of the crawl space wall). Any suggestions?
    • CommentAuthorgyrogear
    • CommentTimeApr 13th 2017 edited
     
    Since conditioning the crawlspace, I have been able to turn off the infloor radiant electric. The later consumed around 27 kWh a day, we replaced it with a wood stove that keeps us warm for a lot less than that, perhaps one half less... (also, wood heating is 4 X cheaper for us, than electric !).

    There *is* one large difference in floor temps, in that walking over floor in bare feet, one no longers "intercepts" the warm loops, but that is not much of a loss... when considering that the infloor electric was in any case *warming* the *crawlspace* by a clear 2°C due to downward heat-loss !

    Best insulation for perimeter is XPS, it needs glueing to the wall (not "dot-&-dab") - I stuck mine on in two layers of 50 mm each: first layer stuck to bare blockwork (three courses, 70 cms high) using high-bond hydraulic mortar, slopped onto the wall with a dustpan and brush, and trowelled onto the backside of the XPS boards (2.5 m x 0.6 m). Second coat of XPS glued to first using PVC cement, applied "not everywhere but generous".

    The difficult bit was filling the 10cm gap at the bottom - this was done by jamming blocks of XPS into the gap and sealing with mortar.
    The insulation was then faced by 8 inches of form-cast soilcrete and stone.

    I had 80 cms or so of working height, sounds like you will have a lot less. It was "pretty" KN**CKERING, but worth doing.

    what is meant by
    Posted By: alexoftheorchardunderside of the external walls

    Are the periphery walls cantilevered ? Sounds unusual ! maybe a drawing would help ! (Just wondering if your crawlspace is not the full underfloor area ?)

    Yes, I take your earlier point about the reference being "US" - most of them are (or Canadian...); the reason for relying on them, is that there appears to be sparse debate about CS issues in UK (and France for that matter).

    Good luck with the doing of the business !

    oops -- what I did not mention, is I have a flush CS roof with concrete joists and mineral interjoist fillers (which I am gradually "painting" white with said hydraulic cement (for psychological reasons - ambiance and anti-dust/spideryness...) :shamed:
    In fact when working in a CS, it is a good investment to put in A LOT of lighting... and invest in an anti-acarian "bomb" from pharmacy...
    gg
    • CommentAuthorcjard
    • CommentTimeApr 14th 2017 edited
     
    Alex, the first and most important question would really be "what do you hope to gain by insulating your floor?"

    If is an appreciable reduction in the heating bills of a conventionally heated house, there are better places to be using that kingspan. If you have underfloor heating it's a different matter, as preventing your heat emitter from being cooled will make an appreciable difference
  17.  
    Posted By: cjardAlex, the first and most important question would really be "what do you hope to gain by insulating your floor?"

    If is an appreciable reduction in the heating bills of a conventionally heated house, there are better places to be using that kingspan. If you have underfloor heating it's a different matter, as preventing your heat emitter from being cooled will make an appreciable difference


    Comfort, heat loss reduction, removal of cold bridges. The house is heated by a centrally placed multi fuel stove and supplemental convector heaters, and a sun lounge across half of the south side which gives me a good amount of solar gain (better utilising that is another little project, but I'm a while off making it to the front of the house with two bathrooms to install and a kitchen extension to build first). I'm renovating to such a degree that I'm partially rebuilding in places. I could just leave the floors totally uninsulated, but I'd like to end up with a relatively well insulated, relatively cheap to run, dry and sound house that'll last another 80 years. I could chuck more kingspan on the walls, but after losing 7" to new internal studs and insulation I'm reluctant to make further sacrifices of space in this room.
  18.  
    Posted By: gyrogearBest insulation for perimeter is XPS, it needs glueing to the wall (not "dot-&-dab") - I stuck mine on in two layers of 50 mm each: first layer stuck to bare blockwork (three courses, 70 cms high) using high-bond hydraulic mortar, slopped onto the wall with a dustpan and brush, and trowelled onto the backside of the XPS boards (2.5 m x 0.6 m). Second coat of XPS glued to first using PVC cement, applied "not everywhere but generous".


    I've got plenty of kingspan and some EPS lying around, what makes XPS better for this application? I suppose I'd fix with adhesive foam and foam the edges. There's only about 250mm of wall to the dirt, so very little product needed compared to a full underfloor job. Surprisingly, I can just about move around under there!

    Posted By: gyrogear
    what is meant by
    Posted By: alexoftheorchardunderside of the external walls

    Are the periphery walls cantilevered ? Sounds unusual ! maybe a drawing would help ! (Just wondering if your crawlspace is not the full underfloor area ?)


    The periphery walls are brick up to the purlins, countered with joists above. The floor and timber studwork elevate up from here, leaving a 2" or so gap between brick and joist. Quite normal, only such a build would typically have a rim joist covering the joist ends, this one doesn't, nor is there a continuous sill plate / purlin / bearer to the outer walls, as explained. There was a thin strip of timber covering the joist ends, and then weatherboards to the exterior, but both bottom external boards had rotted away entirely in to dust due to the impervious (possibly 1:1) render at the bottom of the now removed pebble dashing. This area has been covered by Tyvek and a fascia board so that the area is both waterproofed and accessible (fascia screwed in). The other side of the house has EPS EWI so far, down to the ground, and any dodgy weatherboards were replaced prior to the EPS with OSB.

    Posted By: gyrogear

    Yes, I take your earlier point about the reference being "US" - most of them are (or Canadian...); the reason for relying on them, is that there appears to be sparse debate about CS issues in UK (and France for that matter).



    Yes I think you're right. We seem to have a very narrow perspective in the UK. There's a girl doing a PhD in the subject in Sheffield though, I'm interested to know what she publishes.
    • CommentAuthorgyrogear
    • CommentTimeApr 14th 2017
     
    Posted By: alexoftheorcharda sun lounge across half of the south side which gives me a good amount of solar gain


    a good place to dump some of that solar gain, would be under your floor !

    but U gotta insulate those peripheral bits first :cry:

    gg
  20.  
    ''There's a girl doing a PhD in the subject in Sheffield though, I'm interested to know what she publishes.''

    If it's the one I am thinking of (an I have forgotten her name) she has already completed it, I thought. I left my name with her for a copy of the abstract, but I have not heard back yet (nor remembered to chase it).
    • CommentAuthorgyrogear
    • CommentTimeApr 14th 2017
     
    could this be the lady in question ?

    http://www.sofiepelsmakers.com/suspended-timber-ground-floors.html

    (as in "Sophie's Joist").

    gg
  22.  
    Yes, that's her. I'm interested to know the full extent of her findings but there's not much published online.



    Posted By: gyrogear
    Posted By: alexoftheorcharda sun lounge across half of the south side which gives me a good amount of solar gain


    a good place to dump some of that solar gain, would be under your floor !

    but U gotta insulate those peripheral bits firsthttps:///newforum/extensions/Vanillacons/smilies/standard/cry.gif" alt=":cry:" title=":cry:" >

    gg


    That space does get absolutely freezing in the winter though, being half height single glazed to all three sides. It's getting done at some point, but it's a long way off. Perhaps openable vents in both the sun lounge and lounge which can be switched around depending on the seasons, but that seems unnecessarily complicated. A further consideration is that I intend to let the place out for a year or two at some point, so whatever system is in place will need to be tenant proofed.

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