MortarThePoint

Mortar: Another example of 'repeating' thermal bridging is the mortar joints in block or brick walls. Whilst you might be using thermally efficient blocks for your walls, the mortar needs to be considered as well. In a standard blockwork wall the mortar accounts for 6.6% of the area of the wall. A good thermal block may have a thermal conductivity of 0.11 W/m.K, but mortar has a thermal conductivity of around 0.72 W/m.K. Forming a simplistic average, the mortar increases the thermal conductivity of the blockwork leaf to 0.15 W/m.K (0.11*93.4% + 0.72*6.6%), a 37% increase. Even for a less thermally efficient block of say 0.3 W/m.K, the mortar will increase the overall thermal conductivity of the blockwork leaf by almost 10%. Thermally insulating mortars are available that claim thermal conductivities five times lower than standard. That would effectively eliminate the effect of the mortar on the thermal conductivity of a wall using good thermal blocks (0.11 W/m.K). As most of the performance of a cavity wall comes from the insulation, the overall effect of the mortar is likely to only affect the U-value of the wall by 2-10%. For example a 100mm cavity filled with 0.032 W/m.K insulation with good thermal blocks (0.11 W/m.K) either side would have a U-value of 0.19 W/m2K, if it wasn't for the mortar thermal bridging. With standard mortar, this would be raised by 10% to 0.21 W/m2K. A similarly constructed wall with a 200mm cavity would have it's U-value raised by 6%. I'm using a relatively simplistic approach here, if someone has more accurate figures or experience of using thermally insulating mortars then please comment.

I can't correct it above, but made a mistake. If someone else has the power to correct it great, otherwise it's here. Wall ties: I can't find figures for these, please contribute if you have some, so here is a rough calculation. Wall ties are typically made of stainless steel and might have a cross section area of around 6mm2. At a density of 2.5 ties per m2 they account for a very small proportion of the area (~15ppm), but have a much higher thermal conductivity that the wall insulation (e.g. ~500 times higher, 17 vs 0.032 W/mK). Consequently, their thermal effect can approach 1% (15ppm*500=0.8%). U-value calculations often ignore corrections that amount to less than 3% of the uncorrected U-value of an element (allowed by BS EN ISO 6946).

We all put in a lot of effort considering different insulation types and thicknesses as well as airtightness and MVHR, but thermal bridging (aka cold bridging) could get neglected or forgotten at the design stage. I had a quick look and couldn't see a thread on the general topic of thermal bridging, so thought I would start one. I am far from an expert here, but wanted to draw together some of what I have learnt and prompt other more experienced members to pitch in. According to Designing Buildings Wiki : "A thermal bridge (sometimes referred to as thermal bridging, a cold bridge or thermal bypass) describes a situation in a building where there is a direct connection between the inside and outside through one or more elements that are more thermally conductive than the rest of the building envelope. ... Thermal bridges can be categorised as 'repeating' for example where wall ties regularly bridge the cavity, or 'non-repeating' such as a wall junction or lintel." 'Total fabric heat loss' is the combination of heat lost through different areas of material (sum of each area multiplied by its U-value) and thermal bridges. Thermal bridges can account for a high proportion of the total fabric heat loss (e.g. over 20%). Neglecting thermal bridges at the design stage could undermine the effort you put in on the area based fabric heat losses (e.g. using wider cavities or triple glazing). non-repeating Thermal bridges are typically at interfaces and so have a linear, rather than area, nature. Consequently, they are accounted for in SAP Assessments on the basis of their PSI values, which represents how lossy they are per metre, and their total linear length. It's similar to the area based fabric heat loss which is a sum across types of area multiplied by their U-value, but it is a sum over lengths multiplied by PSI values. Some thermal bridges to consider include: Ends of cavities Lintels Junctions (e.g. between walls and floors, eaves etc) Holes for pipes Wall ties Poor window frame placement Ends of cavities: It is standard and required practice now to use cavity closers rather than masonry closure. This makes for a huge reduction in thermal bridging around windows and doors. Different cavities closers are available with different insulating materials and performance values. Lintels: A standard "Steel lintel with perforated steel base plate" can have a PSI value of 0.36 W/m.K. Considering all the windows and doors in a house design shows that there is a lot of length to lintels. A single metre of such a lintel looses more heat than 2m2 of 150mm cavity wall (U-value 0.17 W/m2K). The difference in U-value between a double glazed and triple glazed window might be 0.4 W/m2K. That means for a 1m x 1m window, more heat is lost through a standard lintel than is saved by using a triple glazed window over a double glazed window (1.3m*0.36W/m.K > 0.4W/m2K*1m*1m). Thermal break lintels can reduce this PSI figure by more than a factor of 5 to under 0.06 W/m.K. In the example of the 1m x 1m window that is an equivalent saving to using triple glazing over double glazing. Obviously triple glazing and a thermal break lintel would give a higher saving still. Wall ties: I can't find figures for these, please contribute if you have some, so here is a rough calculation. Wall ties are typically made of stainless steel and might have a cross section area of around 6mm2. At a density of 2.5 ties per m2 they account for a very small proportion of the area (~6ppm), but have a much higher thermal conductivity that the wall insulation (e.g. ~500 times higher, 17 vs 0.032 W/mK). Consequently, their thermal effect can approach 1% (6ppm*500=0.3%). U-value calculations often ignore corrections that amount to less than 3% of the uncorrected U-value of an element (allowed by BS EN ISO 6946). Useful links: http://www.zerocarbonhub.org/resources/reports/thermal-bridging-guide

Whilst it is good to heat, I meant good to hear ?

Good to heat Iceverge! Please let us know how you get on with the trial holes if you do those.

Must be the hollowcore concrete flooring then

Yes got some windposts as well ?

Specified by the Structural Engineer as we have some long runs without perpendicular walls or bracing and concrete first floor

Can anyone recommend a good alternative for 10.4N blocks as Fibolites only go up to 7.3N? Aglite Ultima also made by Plasmor aren't as good thermally and they can have some odd constituents that I wouldn't want in the living space. Fibolite 7.3N k=0.28W/mK Aglite (special order) 10.4N k=0.36W/mK Stranlite 10.4N k=0.43W/mK

Yes sealing of the cavity will need to be pretty good as otherwise I can imagine millions of beads going everywhere. Calculating how many beads are involved is mind boggling.

Well we've surprised ourselves here because we think we will got with the Ecobeads. The U-value is essentially unchanged (Ecobead platinum lambda=0.033W/mK vs Dritherm Ultimate lambda=0.032W/mK) and I have quotes for confidence on the price. We talked to some insurers to see if there were any concerns, of which there was none. I think the factors that swayed it were: Intrinsic water handling - drains rather than dries. No on site storage - I would have worried about the fibre batts getting wet and they would have taken up space as well as being a marginal theft concern. Ease of wall construction - No fibre batts to put in correctly. I'm going to get guidance from the installer about how to build with beads in mind to make sure that things like cavity trays fill up with beads nicely. We are trying to build with a low chemical (VOC) approach and liked that the Knauf Dritherm used their Ecose technology that was Formaldehyde free. We ruled out PIR for chemical reasons. I will double check with Ecobeads that they are equally good in that regard. We're far from obsessive about this sort of thing, but would like to preserve air quality in the house as we are reasonably rural.

I've got 100mm cavities so not particularly wide and they've quoted on that basis.

Did you worked along side the brickies then or did they build up the walls to the point ready for you to install in the evenings? It would need to be the platinum ones to give equivalent Uvalue. The price seems to be the same as fibre batts 32.

I'm still pulled in two ways on this. If I could be certain they were installed correctly, I think I'd go with the Knauf Dritherm Ultimate fibre batts as they are more 'normal'. Blown beads could give a possible future purchaser concerns since there have been horror stories associated with their retrofit use. I like the labour saving of the blown beads and the fact that it wouldn't need the constant monitoring of how the insulation is installed that fibre batts would require. That said, if they mess it up on the day of blown bead install then it would be a nightmare. These decisions often come down to minimising the downside rather than optimising the upside. Maybe that sounds a big 'glass is half empty', but you don't get giddy about your cavity insulation being slightly better than it could have been, but you would get sick of it being a lot worse.

I watched the US video below that talks of locally thickening to 6", ie 150mm. As we are having an insulated floor I'll need to double check though. https://www.bendpak.com/car-lifts/concrete-floor-requirements/ https://www.gregsmithequipment.com/2-Post-Lift-FAQ-Concrete

A moderate saving then, but worth having

Everywhere they were supposed to or coming out and making a mess? Good to hear some positive experience with the product.

I've seen videos of installers tweaking the glue recipe, so it doesn't seem an exact science. Voids and or settlement are concerns and you wouldn't be able to see if they had happened.

I guess so, but brickies who make no concessions to the the approved installation method wouldn't save much time if not fitting them.

I was surprised, but the beads installed seem the same price as just the material cost of fibre batts.

Well I thought I knew exactly what we were going to do for cavity wall insulation years ago, but just before placing the order for the fibre batts I (re?-)discovered blown beads (Ecobeads). I don't know if the Ecobeads have got better in the last 2-3 years since we decided on Knauf Dritherm Ultimate 32, but they look quite attractive. I got some quotes and the price for Ecobeads installed is essentially the same as the Dritherm material cost. I'm finding it difficult to make up my mind now. Some pros / cons: Kingspan did a white paper on fibre batts and, whilst they have a commercial interest in knocking full fill insulation, they do make some good points. I haven't seen many sites, but I don't think I have ever seen people installing fibre batts as set out in their BBA documents. Outer leaf first, snot boards and properly orientated batts. I have seen loads of YouTube videos of clearly skilled brickies who don't follow much of this and if you look carefully are dropping and leaving snots on the batts. I don't want to be a nightmare for my brickies breathing down their necks and insisting they work in a way they don't normally, but I'd want fibre batts installed as per the BBA certificate as otherwise there can be a loss of performance even if not an actual damp problem. There were loads of bodged blown bead installs for retrofit, but I'd expect that is due to narrow cavities as well as other unsuitability issues. I don't like the thought of them and any future work could mean beads blowing about for years to come. I also worry about insects living in them as I have seen that with PIR insulation. There is also a lot of faith in that one day of install. If the installer is a joker then you're stuffed whereas a more gradual install can be understood and rectified much more easily. We're building in East Anglia so it's the best part of the country for fibre batts, but still. Blown beads feel like a no brainer for large cavities (e.g. 200mm or more) but I'm not so sure for us (100mm cavities). Your help and experiences please making this decision would be massively helpful.

Bit late to the party here, but our Structural Engineer specified Kingspan GG300 for our garage as it has higher load bearing It has Compressive strength = 300 kPa (at 10% compression) https://www.kingspan.com/gb/en-gb/products/insulation/insulation-boards/kingspan-greenguard/kingspan-greenguard-gg300

Thanks, good timing to have he input as we haven't poured yet so still an option to change.

Are you sure they count as an AAC block? They aren't foamed concrete, but are an aggregate block. The aggregate is foamed/aerated though: "Expanded clay nodules are produced by sophisticated pyrogenic technology whereby geochemically specific clay is expanded in a rotary kiln at high temperature." but it claims to be "Class 1 aggregate as defined in BS 5628 -3"

I'm thinking of swapping to Fibolite blocks. When I first heard of them they sounded a bit 'high tech' for my reasonably traditional approach to the superstructure. I was also wary of cracking concerns having heard of it associated with other thermally performant blocks. Whilst Fibolite blocks help with U-values, the absolute requirement in my mind for the blocks to perform their structural role and I'm not wanting to make any sacrifices there. I'm sure like all self builders, I want my house to still be standing in a couple of century's time ?. What do people think, does anyone have anything to say against Fibolite blocks?