If in Doubt, Insulate It

When we first discussed with Bill Butcher of Green Building Company the insulation techniques required for our house, using innovative materials was the last thing on our minds. We had assumed, in our naiveté, that Kingspan was our only option. We were so wrong!

I freely admit I don’t really understand what U-values are; I had never heard of interstitial condensation; I didn’t know that houses were supposed to breathe.

As the design of the renovation took shape, it became clear that our particular combination of extreme environment, solid walls, and rain penetration would require something more radical than just sticking Kingspan on the walls and hoping for the best.


Innovative materials
Bill researched the available materials and found that the German company Knauf Aquapanel had been supplying an innovative product for passivhaus building, called TecTem. TecTem is made from perlite, an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. When heated to 900degrees Celsius, the water is driven off and the perlite expands, giving a lightweight material with the additional property of being able to absorb and dispel water. It is mold-resistant, fibre-free, eco-friendly, and completely recyclable. It has excellent thermal properties and breathability. It would be ideal for use in the barn part of our house, where the solid walls and lack of damp proof course mean that we have problems with moisture; moreover, the ground floor suffers from rising damp in one corner. Just one snag; TecTem is not currently available in the UK. But Knauf were interested in working with us to provide a solution to our problem and supplied us with the TecTem direct from Germany. In return, we are supplying them with data on the performance of the product. Within our walls, buried behind the insulation as well as attached to some of our beams, are over 50 moisture and temperature sensors. These report wirelessly to an Omnisense monitor that transmits the data gathered to a central database where it can be analysed, coordinated by Tim at the AECB. We are really excited that our project to give us a warm home will help future builders and architects to choose the right materials.

I have already written about the use of Foamglas in preventing thermal bridging on our steel i-beams, and its use as a tanking material along our dampest wall. In addition to TecTem and Foamglas in the barn half of the house, we have another Knauf product, Thermoshell, on the walls of the 1990s extention, that is in the kitchen, living room and master bedroom. Thermoshell consists of two parts. First, on top of the parged stonework, horizontal studs are fixed, comprised of very high density foam called XPS with a layer of OSB chipboard on the outer face. The whole stud is 100mm thick. In between the studs, 100mm batts of Earthwool mineral fibre are fitted. The whole is then covered by a sheet of Intello and a service void is constructed on top using ordinary timber 2×2, with plasterboard and plaster skim completing the wall. Of course, this does have the effect of reducing the dimensions of the room by about 120mm per wall, but once completed the difference in size is not noticeable.


The really interesting thing about the wall treatments, whether TecTem or Thermoshell, is that the insulation and plasterboard is not just taken down to the floor on each level; it is carried down the whole height of the house in one continuous layer.  The floorboards along the edges of rooms were removed to facilitate this, and where floor joists impinged they were remodelled and ruthlessly taped for airtightness; stud dividing walls were cut away from their junction with the outer walls or removed altogether and rebuilt on top of the continuous insulation. This method ensured that there are no breaks in the insulation and the whole house is warmed as a consequence.

Bill Butcher has blogged about the technical choices for insulating our home on the Green Building Company’s website.

The third innovative material to be used in the house are Vacuum Insulation Panels (VIPs). These panels are attached to the inner embrasure of each window and external door. They were necessary to minimise the depth of insulation around each window where the window could not be enlarged. Our windows were mostly originally cut into a windowless barn, and were made deliberately quite small. The few windows in the newer extension were made to match the small size. We had had new Ecoplus doors and windows installed some years previously and so could not feasibly have the openings enlarged. Moreover, enlarging them would have required bigger lintels and the whole project would have just got completely out of hand! Vacuum panels were the answer.


VIPs do require special handling. They are made to measure for each flat surface of each opening; they cannot be pierced, and so have to be stuck in place; any other covering material, for example window boards or plasterboard, have to be similarly fixed with adhesive. A far as aftercare is concerned, we do have to be careful not to puncture the panels, so roller blinds fitted into the embrasures are not allowed; but otherwise there is no problem as they are protected by window boards and plasterboard. They are only 10mm thick but have the insulating property of other insulation material that is 100mm thick. More technical information can be found on Bill Butcher’s blog.


The U-value is the overall heat transfer coefficient that describes how well a building element conducts heat or the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure.

Interstitial condensation is a form of structural damping that occurs when warm, moist air penetrates inside a wall, roof or floor structure, reaches the dew point and condenses into liquid water.

For other posts in this series, see:
Our House Reborn
Airtightness and Ventilation
Water, Water Everywhere
Renewables in a Low Energy House


1 Comment

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One response to “If in Doubt, Insulate It

  1. Pingback: Home Sweet Home; or There and Back Again | Things my grandma taught me

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