Jan 202018

As a companion to the report Winter Cold Virus Hits the Workforce!, this blog describes the last two weeks of our building work.
so with the background noises of coughing, sniffing, sneezing and talking with croaky voices, we have been analysing the design of our Glazing Framework for the Skylight. We are thinking of reducing the number of glazing wooden rafters from the regular 600mm spacing to more like 1000mm instead. This would make the aspect of the skylight more pleasant to look at and to look through too. It would mean less physical number of elements to construct, assemble and install.

Structural Analysis

But first, we had to analyse the structural requirements of our roof to make sure the glass can take the strain and loading of various weather conditions, like for example, a foot of snow or gale force winds, as specified in the Building Regulations for our easterly region. The result of that research was that our primary glazing layer needs to be 6mm toughened glass, spanning the 1200mm by 1000mm of support.

Size and Spacing

Next, we took each section of the Skylight in turn, to adjust the size of the glass so it is a regular spacing, for each room upstairs, taking into account the maximum we are allowed as per calculation of research we did, as follows:

  • Great Room: 1 module – 1200mm and lots of triangular pieces
  • Spare bedroom: 4 modules – 1011mm
  • Hall & Stair: 2 modules – 813mm
  • Study: 2 modules – 1008mm
  • Workshop: 5 modules – 1061mm plus more triangular pieces

The other side of the skylight (where our solar electric collectors are located), starts with more triangles and a 1200mm section over the great room then a regular spacing of 917mm most of the way along the whole length, in 13 modules followed by a last few triangle pieces. This deliberate design choice allows us to fix and clamp the sloping wooden rafters right through the ridge beam for extra strength and security and allow

Thermal Properties

the solar panel modules to all the same size.
Another part of our analysis we have been doing, is the thermal properties of these glazing units, whether the cost of double or triple, or even quad glazing would payback and how quickly. Plus, the added complications of wear and tear to these sealed glazing units, during a hot and cold heat cycle and that causes physical stresses to the joints that seals the layers of the glass panes together. Thermal expansion is one of the most powerful forces out there and there is nothing anyone can do to stop it, apart from engineering the joints and seals to cope with the stress and strain of this physical effect.


At this moment, the results of our research in heat loss, the weather conditions and thermal properties of the various glazing options, here is a summary (for the whole Skylight):

  • Heat Loss: 12050 kWh per year using a 10 year historical data
  • Energy Cost: £1205 per year with single glazing
  • Double Glazing extra: £2000 to buy but Energy cost cuts dramatically to £140; payback time is 2 years!
  • Triple Glazing: £3000 to buy; £85 per year for energy; 3 years payback time
  • Quad Glazing: £4000 to buy; £60 per year; 4 years payback time.
NOTE: One aspect of this research that have not been included in these calculations, is the Solar Gain factor. This is a very powerful energy source and our Skylight is very large and will be collecting a great deal of solar energy during the daylight hours and we haven’t incorporated this into our calculations. But roughly, it will save us even more money and the payback time would reduce even further!

These payback times are all based on a fresh start as the building is constructed, but it would be a completely different story if after 20 years, we have to replace the glazing units and it would be a pure fixed cost spread over the lifetime of the product. Everything fails eventually so one has to get into the frame of mind that we should be saving some money away in a piggy bank so we are ready for the replacement. Glazing units are now given a lifetime of 20 to 25 years so if it costs £4000 up front, then we need to put away £250 per year for 20 years, as no doubt the prices will rise too! eeek!
Our next job is to translate all this into a construction plans, building an order for materials and plan procedures etc.

 Posted by at 6:22 pm