Building Regulations 2010 - Part L

[kurnal]

A building designer is insisting that under the new SBEM regulations and conformance to part L2 (2010) we must install translucent rooflights in a large new warehouse building. We dont want to.
I am struggling to see where he is coming from - the only references I can find to rooflights are in respect of solar gain. Anybody able to enlighten me please?

[Tom Sutton]

Kurnal maybe its not about heat it could be about light more natural light less artificial light, reduction on the carbon footprint. It would depend on how the SBEM calculations are done.

[kurnal]

Yes thanks Tom thats what the designer is suggesting but its outside my area of knowledge. The client specifically does not want rooflights for lighting, the UV damages stock, the warehouse is too high for the light to reach picking levels, they will soon get dirty and need cleaning which means roof access equipemnt,  and will not help at all underneath the  mezz .  So artificial  lighting is essential and this can be achieved with a high tech solution. The designer is insistant that such buildings have to have roof lights, it sounds odd to me I would have expected that in common with most Building Regulations the carbon performance of the building would have been a functional requirement rather than a prescriptive one.

[AnthonyB]

Perhaps the client should get a new designer!

[Tom Sutton]

Kurnal to prove your case you would need another set of calculations and cert to contradict the designer maybe a word with one of the companies that provide the calculations would help.

[John Webb]

Would an approach direct to the BCO for the area where the building is to be erected pointing out the client's problems with roof-lights perhaps get you a waiver?

[CivvyFSO]

I read it the same as you Kurnal. If anything, ADL seems to want to minimise the amount of glazing on the ceiling due to potential solar gains. The rooflights also have a much higher u-value, therefore more heat will be lost through these. This would quite possible easily account for any 'savings' made in lighting, which will be practically zero anyway, as people are not going to switch less lights on just because there are some rooflights provided.

It seems that the reference case for solar gains does assume a certain percentage of the roof being rooflights, but this is only a reference case to give a starting point for any calculations.

[wee brian]

Part L is essentially performance based rather than a functional requirement (like Part B). There is a prescribed method of calculation (SBEM) and a minimum performance value. As such a waiver isnt really an option.

Theres nothing that would make you install roof lights but it will help with the lighting part of the Calcs. I doubt it's a big problem but you need somebody that can work SBEM to check.

[kurnal]

Thanks so much for your help.

I understand as well as building designs meeting overall CO2 emissions targets, individual elements of the design have to meet minimum standards, or "backstops". In order to meet the Target Emission Rate, designers would typically have to select elements that are considerably better than these standards, for example minimum efficiencies of boilers, chillers, air distribution systems and lighting.

It appears that if the lighting failed to meet the backstop standard, (simply because the backstop standard for comparison incorporated an element of natural light) it would not be possible to trade off  or compensate for the weakness by providing an improved performance in another backstop standard say roof insulation even if as a result the building had a much smaller carbon footprint?

It appears to me that the backstop  standard may be appropriate for a speculative build shell only design but where a bespoke building for a specific use and to the clients design is proposed there should be more flexibility. Nobody - or the environment- is well served by the installation of unnecessary and unwanted equipment.

I understand that there are subdivisions of the different purpose groups within the SBEM calculations including one called a process warehouse with a different backstop standard to a storage warehouse for lighting.

[Owen66]

Adding rooflights to a warehouse is an easy way for a designer to meet the targets in Part L 2010. For big sheds, adding rooflights causes a reduction in enegy consumption for lighting in the notional building and makes compliance with teh target rate easier.

Perversely, the reduction targets for 2010 were 22% for sheds without rooflights and 36% for those with - however the with rooflights notional building doesn't lose that much more heat but does see significant benefit from the lighting reduction.

So designers just jump on the inclusion of rooflights as an easy win - if you take them out they need to put more effort into teh wall and roof performance (more insulation) and making the shed more airtight.

So essentially, you dont have to have rooflights to comply with PartL in the SBEM model, it's just harder to do so if you don't have them.

I would get the designer to re run the SBEM model without rooflights and then tell you what fabric improvements will be needed to get you through Part L without roof lights - it's a bit more effort but no real drama - I've just done exactly that where a client didn't want roof lights for security reasons, so it can be done with minimal effort

Regards

Owen