PLQ 3.4 – Inspired Improvements

Hello BIMfans,
By writing PLQ 3.4 – EPConclusion, I was able to complete the calculations for my Energy Performance Certificate (EPC) Rating.  Having made this information readily available, I issued a challenge to see what thermal improvements you would suggest.  I’m glad to say I received a plethora of suggestions (thank you everyone!) and have included the most detailed suggestions below.

NOTE:  To ensure that these suggestions were as realistic as possible, I have aimed to achieve the minimum requirements set out in the Welsh Approved Documents.  While I could have considered a higher benchmark such as enerPHit, I wanted to ensure that I could afford and justify the improvements described below, so they might actually be implemented.

Floors and Roofs (+5 SAP points):

This suggestion came from Craig Hardingham of MLM, who felt I would benefit from insulating between by floors and roof joists using a product like Rockwool.

Regulations:  According to the Welsh Approved Document L1b, I need to achieve a maximum u-value of 0.25W/m²K if I upgraded the thermal performance of my floor and 0.16W/m²K if I upgraded the performance of my roof.  While there are plenty of high-performance insulation materials, Rockwool is an excellent suggestion for two reasons:

  1. It is a mineral fibre, so if I use it between my joists it would keep the assembly breathable and the Rockwool can accommodate any warping or shape variation;
  2. Rockwool are good Welsh firm!

For my floor, I have chosen ROCKWOOL FLEXI.  Using my graphical model, I am able to calculate the perimeter and area of my floor to determine a P/A Ratio of 1.2, which means I need 140mm of ROCKWOOL FLEXI to achieve the desired U-value.

For my roof, I have chosen ROCKWOOL Roll, Twin Roll and Rollbatt.  If I cross-layer the insulation I would need a total of 270mm to achieve the desired U-value.

Modelling:  To undertake both of these calculation, I don’t need to edit my geometry, but I do need to add new properties to capture the thickness of my insulation. I couldn’t find an ideal property within the IFC Data Schema, so I have made my own:


NOTE:  I used -thickness because of xBIM doesn’t export properties with -Width, -Height, -Length suffixes to prevent duplication of information between different worksheets.

By placing this property onto my levels, I was able to get it into COBie to form part of my calculations without altering the exclusion list.


SAP:  For SAP Calculations, floor U-values (28a) are calculated based on a bespoke formula.  With an assumed thermal conductivity of 0.035 W/mK, the Rf value of my floor would increase to 4 instead of my default 0.2.  In addition, I would also seal my floor reducing the floor infiltration rate (12).  For my roof U-value (30) a new figure of 0.16 W/m²K is taken from table S9.

Based on the above, upgrading the insulation in my ground floor suspended timber floor and roof would improve my SAP score by an impressive five points.

Walls (+6 SAP points):

This suggestion came from John Hefford of Thermal Economics, who felt I would benefit from thermal dry-lining using Alrefelx Platinum while Emma Hooper of Bond Bryan Digital felt I would benefit from using Properla’s Masonry Creme.

Regulations:  According to the Welsh Approved Document L1b, I need to achieve a maximum u-value of 0.30W/m²K if I upgraded the thermal performance of my external walls.  To be honest, I hadn’t considered dry-lining however, due to my solid walls and flush fascia, cavity-fill and external wall insulation (EWI) systems are not feasible. Luckily, as John suggested a high-performance dry-lining system, I would only need 75mm to achieve the desired U-value.  Also, thanks to Emma’s suggestion by combining Alrefelx Platinum with Properla Masonry Creme, I would (in theory) only need 65mm.  This is because, while they have no BBA certificate demonstrating this, Properla has shown to improve the thermal conductivity of masonry to 0.355K (w/mK).

Modelling:  Post-installation, someone like  Thermal Economics could do a U-value test to provide to the SAP Assessor.  Otherwise the SAP Assessor would assume a much worse U-value of 0.6W/m²K.  This value would be place on my wall elements, but they would not appear in COBie, as such I would instead reference the test results and manually input this information.

NOTE:  I could cheat and place a property like ‘WallThermalConductivity’ onto the house, but this defeats the object of having a schema.  I’d like to remind you all that documents are not taboo in BIM!

SAP:  For SAP Calculations, the Wall U-value (29a) would use a new figure of 0.3W/m²K, and the walls heat capacity (29a) would also need to be updated to 9 kJ/m²K.  In addition I would need to remove 0.517m² from the ground floor area (1b) and 0.788m² from the first floor area (1c).

Being a mid-terrace home makes internal insulation much more efficient

Based on the above, treating and dry-lining my external walls would improve my SAP score by six points.

Windows (+2.5 SAP Points):

This suggestion came from Natasha Jayne Vermeulen of Whittam Cox Architects, who felt I would benefit from upgrading my windows using FORMAPLUS from Rationel.

Look at it, it’s like a work of art!

Regulations:  According to the Welsh Approved Document L1b, I need to achieve a u-value no worse than 0.16W/m²K when upgrading my existing windows.  Luckily, FORMAPLUS provides a U-value of 1.29W/m²K; making it an ideal solution.  Also, I love the look of wooden windows with an aluminium facade!

Modelling:  I discovered that Rationel have their windows on BIM Object.  However, these objects are quite frankly useless.  For example, the object I chose included a property called ‘U-value’ (should be ThermalTransmittance) which is formatted as text, instead of a number.  Meaning that it’s value ‘0,8’ (note the comma) doesn’t respond to project units, cannot be used for analytics and breaks my SAP Calculations!  So, I just used my own objects instead and added the properties I’ve previously discussed.

With objects like these, who needs enemies!

SAP: For SAP Calculations, now that I have updated the properties in my model, I am able to update my window U-values (27) to reduce heat loss and their G-values and Frame factors (74-82) to adjust solar gain.

Based on the above, replacing my windows with Rationel  FORMAPLUS would improve my SAP score by two and a half points.

Boiler (+4 SAP Points):

This suggestion came from Darryn Marrs of Jonathan-Rhind Architects, who felt I would benefit from upgrading my boiler to biomass or a high-efficiency gas boiler.

Darryn was kind enough to make a suggestion but unfortunately didn’t suggest a product.  So, I decided to have a look at the Building Energy Performance Assessment support website, which includes the relevant product data to inform my SAP Calculations.  Using this site I was able to select the Worcester, Greenstar CDiNote:  I have a Worcester Greenstar, so (in theory) choosing another Greenstar should ease this process.


Regulations:  As I am not intending to move my flue or change the position of my boiler, I do not believe there are any regulatory issues I need to consider. (Phew!)

Modelling:  I couldn’t find a BIM object for this boiler, so I used my current boiler family and increased the boilers size to suit and updated OperationalEfficiency to 90.

To be honest, I still think my boiler’s geometry is too complex

SAP:  Now that I’ve updated my model, Boiler efficiency (206) and (216) are significantly improved  to 90 and my boiler’s electric load (230c) has been reduced down to 30kW/year.

Based on the above, replacing my boiler with a Worcester Greenstar CDi would improve my SAP score by four points.

Sum Total:

Amazingly, if I did all of the improvement works identified above, my SAP Calculations would go from 66 to 81.5.  This is a 15.5 improvement, bringing  Tŷ Crempog from an EPC of D to B!!  Note:  Those of you who kept count would have noticed that my improvements add up to 17.5, not 15.5.  This is because improvement to my external floor, wall and roof insulation mitigates the gains from a more efficient boiler; improvements need to be considered holistically.

Jump Crempog, Jump to a more sustainable home!

And there we have it.  With these inspired improvements based on my SAP Calculations, I now know what work can be undertaken and have enough information to collect quotations.  This means that my final Plain Language Question, PLQ 3.4 is complete!

Operation and Maintenance

  • 3.1 What are the sizes and condition of the windows & doors?
  • 3.2 What assets are in a poor condition?
  • 3.3 What costs can be attributed to my assets?
  • 3.4 What are the most cost effective thermal improvements that could be undertaken?

Now that all of my Plain Language Questions have been completed, I should probably look to undertake some of these improvements…

Note:  If you have any comments regarding these inspired improvements, then please let me know either on Twitter, or by commenting below.

2 thoughts on “PLQ 3.4 – Inspired Improvements

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