UK Building Reg's, Part L - U value Calculation - Help required

[JTDTimberframe]

Hi Folks,

Anyone here workin the UK and familiar with U Value Calculations? I'm after a good guide / overview of the design process for calculating U Values. Can anyone help / reccomend a good guide?

Thanks

Stephen Napper BEng(Hons) AMIMechE

http://www.jtdtimberframe.co.uk

 

[Ussuri]

I take it you mean the Building Regulations 2000 as opposed to the Building (Scotland) Regulations 2004. The Building Regulations are only applicable in England and Wales.

In Scotland (Guess where i'm based) the Scottish Building Standards Agency publish Technical Handbooks which give you advice on how to best meet the requirements of the Regs. The link below takes you to the guides. I would assume there is something similar for the English Regs.

http://www.sbsa.gov.uk/current_standards/tbooks.htm

Our system is slightly different to yours in that we dont have to submit calculations to the Building Control Department provided the calculations are signed of by an Engineer who works for a Nominated Company, and has been vetted by the SBSA. If I understand the English Regs, you have to submit all calculations regardless.

A useful link is to:

http://www.opsi.gov.uk/legislation/uk.htm

Here you can search for all statuatory instruments on line, for instance.

http://www.opsi.gov.uk/si/si2000/20002531.htm

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Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
Archimedes

 

[Ussuri]

Had another thought, a couple of textbooks/reports which might be of some use are:

The New Metric Handbook by David Adler;
Housing Design Handbook published by the Building Research Establishment 1993.

The latter is a bit out of date but it did contain some good information.

 

[tonyuk]

The procedure is explained in the L1 Approved Document which is available from the ODPM web site odpm.gov.uk. It's very simple until you get to constructions with alternate heat paths (e.g. insulation between timber studs). You might also check out our SuperHeat program

http://www.sda.co.uk/shw.htm

Note to anyone not from the UK reading this thread: U-value calculations work out the thermal conductivity of a constructional element such as a wall, floor or roof. Nothing to do with structures, though in my building inspector days a well-intentioned clerk saw 'calculations' on the front sheet of U-value calculations and promptly sent them off to our consulting structural engineers for checking!

 

[JTDTimberframe]

Tony,

Guess what I'm designing? Timberframed buildings with insulation between the studs!

Thanks for your tip on your software, but I've found it already through Google. Actually looking for a printed book / web page type of thing so that I can understand what yours, and anyone else's software, does behind the scenes so to speak.

Steve

Stephen Napper BEng(Hons) AMIMechE

http://www.jtdtimberframe.co.uk

 

[henri2]

tonyuk, use of R and U values in performing energy calcs for the building envelope are covered by energy conservation codes in the united states. R-Value is the reciprocal of the heat transfer coefficient (U-Value)and I guess its still the same in the UK...no?

 

[tonyuk]

henri2, you've got it. We work on U-values which is the heat loss (W) through 1m2 of wall (etc) with a 1C temperature difference, so the lower the value the better. The US method of R values is simpler in that you just add up the R values of the components.

Where the complication comes is when you have two forms of construction presenting alternate heat paths such as Steve has with insulation between studs. The effect is the same as with an electrical circuit having two resistors in parallel: more heat goes through the lower resistance. In 1995 the calculation method was changed to allow for this, and then changed again more recently with Rupper and Rlower values which I will not try and explain here. The calculation method is explained in the L1 Approved Document 2002 edition appendix B available as a free download from

http://www.odpm.gov.uk/index.asp?id=1130727

 

[henri2]

Bldg departments (building control authorities) around here typically permit a choice of either prescriptive or performance based approaches. The former is usually straight forward and rather conservative. The latter allows for an approved points system or use of approved software which I understand may permit use of FEA.

Use of insulation in the cavity spaces of residential wood (timber) framed walls is common. The insulation is designated an R value...something I learned within my first few days working at a design office in California.

Energy compliance for bldg construction is a very serious issue in the US and a lot of resources have been invested in research and development...findings of which lead to development of cutting edge analytical tools used by professionals in industry.

I have a question on another matter you could probably answer. Do undergraduate civil engineerings in the UK typically offer masonry and timber design as part of the curriculum/syllabus?

 

[Ussuri]

Henri2,

I cant say for any other university, but mine certainly didn't. We were taught steel design to BS5950 and concrete design to BS8110.

We had absolutely no contact with masonry and the only contact we had in timber was to design a bridge in our design practical. Something which proved tricky, not only because we had never been taught anything on timber, but at the time timber design was permissable stress based and two codes we had been taught were ultimate limit state.

On the plus side, we did get taught about mechanical, electrical and electronic engineering as well.

 

[pba]

In regard to U-Values. I've always encountered these as part of the Architects or M&E engineers works and I've never attempted the assessment my self.

JDTimberframe - Are you trying to do too much and exceeding you ability? (Please - This is not a personal criticism).

Ussuri - The English regs do kind of allow for self certification but, dare I say, requires the certifying engineers to jump through more hoops first...

Henri2 - As an undergraduate, I was given a brief introduction to timber and masonry design codes only. For steel and concrete we did non-code specific theory as well as some introduction to the codes. I think it was of some but limited benefit.

 

[henri2]

Ussuri and pba thanks for your responses.

 

[Ussuri]

I must agree with pba, in my experience it has always been the Architects and Building Services Engineers who do the assessment of thermal insulation.