A Build­ing Regs’ Guide to Part L — Get­ting En­ergy Ef­fi­ciency Right in New Homes

The Build­ing Reg­u­la­tions have plenty to say about how en­ergy-ef­fi­cient new homes should be. Paul Hymers sets out the es­sen­tials, from the ini­tial SAP cal­cu­la­tions to the fi­nal En­ergy Per­for­mance Cer­tifi­cate

Homebuilding & Renovating - - Contents - Paul Hymers Paul Hymers is a build­ing con­trol of­fi­cer and has writ­ten eight books on home im­prove­ment and build­ing homes.

Build­ing con­trol of­fi­cer Paul Hymers ex­plains how to com­ply with the Regs sur­round­ing en­ergy ef­fi­ciency when build­ing a new home

Build­ing a new home comes with some ex­tra en­ergy ef­fi­ciency re­quire­ments un­der Part L1A of the Build­ing Regs, com­pared to ex­tend­ing an ex­ist­ing home or con­vert­ing an ex­ist­ing build­ing. (Many such schemes also re­quire SAP cal­cu­la­tions; this ar­ti­cle cov­ers new builds only.)

It’s tempt­ing to think that you can sim­ply ap­ply the max­i­mum U val­ues to the el­e­ments (the walls, roof, win­dows) of your new build and as­sume that the com­pleted house will com­ply with the Regs. In­stead, you have to ex­am­ine the house more holis­ti­cally. For that, SAP ( Stan­dard As­sess­ment Pro­ce­dure) cal­cu­la­tions – the gov­ern­ment’s cho­sen as­sess­ment method for mea­sur­ing en­ergy ef­fi­ciency in homes – are used. Two re­quire­ments must be met: 1 The Fab­ric En­ergy Ef­fi­ciency Stan­dard (FEES) is the pro­posed max­i­mum space heat­ing and cool­ing en­ergy de­mand. This is the amount of en­ergy which would nor­mally be needed to main­tain com­fort­able in­ter­nal tem­per­a­tures and since this is in­flu­enced by the ex­ter­nal fab­ric U val­ues, for out­side walls, floors, roofs, win­dows and doors, this is all about ther­mal in­su­la­tion to the ex­ter­nal en­ve­lope of the build­ing. The FEES must not ex­ceed the Tar­get Fab­ric En­ergy Ef­fi­ciency (TFEE), which is based on a no­tional dwelling of the same di­men­sions with max­i­mum per­mit­ted U val­ues. 2 The Dwelling En­ergy Rat­ing (DER) is much more holis­tic and looks at en­ergy use per

unit of floor area, a fuel-cost­based en­ergy ef­fi­ciency rat­ing ( the SAP rat­ing) and emis­sions of CO ( the 2 En­vi­ron­men­tal Im­pact Rat­ing). Th­ese in­di­ca­tors of per­for­mance are based on es­ti­mates of an­nual en­ergy con­sump­tion for the pro­vi­sion of space heat­ing, do­mes­tic hot wa­ter, light­ing and ven­ti­la­tion. Other SAP out­puts in­clude the es­ti­mate of ap­pli­ance en­ergy use and the po­ten­tial for over­heat­ing in sum­mer with so­lar gains and the re­sul­tant de­mand for cool­ing the home.

The DER must not ex­ceed the TER ( Tar­get En­ergy Rat­ing) which is based on a no­tional dwelling of the same di­men­sions, etc.

Start­ing Early is Key

For new builds, SAP cal­cu­la­tions are made at the de­sign stage to ar­rive at a Predic ted En­ergy As­sess­ment (PEA), which pro­vides a rat­ing of en­ergy per­for­mance based on the de­sign of the house and shows the build­ing in­spec­tor that the home will meet the re­quire­ments un­der Part L of the Build­ing Reg­u­la­tions.

“When the build­ing works are com­plete, the real air leak­age rate will be dis­cov­ered by on-site test­ing”

When the build is near­ing com­ple­tion, air­tight­ness test­ing will be un­der­taken in or­der to es­tab­lish the ‘as-built’ air­tight­ness (or air leak­age rate). Fi­nally, the SAP as­ses­sor will cre­ate an EPC (en­ergy per­for­mance cer­tifi­cate); an EPC is re­quired for homes when built, sold or let. Au­tho­rised SAP as­ses­sors are needed to pro­duce th­ese cal­cu­la­tions and ul­ti­mately your com­pleted home’s En­ergy Per­for­mance Cer­tifi­cate (EPC). As such, you will need to find a con­sul­tant and th­ese are re­ferred to as ‘on build’ SAP as­ses­sors. (The pro­ce­dure and li­cens­ing of th­ese as­ses­sors is dif­fer­ent to that of the as­ses­sors who process SAP cal­cu­la­tions for ex­ist­ing build­ings.) You can search for a reg­is­tered as­ses­sor or check the cre­den­tials of one at: epcreg­is­ter.com.

The cal­cu­la­tion process has to take place early in the de­sign stage, so that the de­sign is spec­i­fied cor­rectly for the ther­mal in­su­la­tion lev­els and heat­ing and hot wa­ter prod­ucts.


Of course the air leak­age rate can only be spec­u­lated at this point, but nev­er­the­less an as­sumed value has to be en­tered at the de­sign stage. Part L1A of the Build­ing Reg­u­la­tions set min­i­mum re­quire­ments for test­ing at a back-stop value of 10m3/hr/ m2 but of­ten the rate needed to hit the TER is much lower. Typ­i­cally, de­sign fig­ures of be­tween 4 and 6 m3/hr/m2 are used and th­ese can eas­ily be achieved with some at­ten­tion to de­tail dur­ing the build. Ei­ther way, when the

build­ing works are com­plete, the real air leak­age rate will be dis­cov­ered by on-site test­ing.

All new dwellings need to be tested on com­ple­tion, with only two ex­cep­tions: 1 If the same builder has pro­duced an iden­ti­cal con­struc­tion in the last 12 months and suc­cess­fully passed an air­tight­ness test. (This does not usu­ally ap­ply to self-build homes); 2 Where a high de­fault value of 15m3/hr/m2 has been used in the SAP cal­cu­la­tion. (If you would like to avoid the worry of site test­ing, you can choose to en­ter a rate of 15 for the air leak­age rate — the equiv­a­lent of leav­ing a large win­dow open dur­ing the test and hence it ex­empts you from test­ing at all . In this case, you will be heav­ily com­pen­sat­ing for it with su­per- thick in­su­la­tion and other mea­sures.)

Ide­ally the test should be un­der­taken when the build­ing is as close to com­ple­tion as pos­si­ble. As a min­i­mum, the build­ing en­ve­lope needs to be com­pleted but does not need to be dec­o­rated or car­peted. Vents are sealed or taped over dur­ing the test — which is look­ing for air leak­age where it shouldn’t be and not where it should. Tra­di­tion­ally this means gaps around the win­dow and door open­ings or the gaps left from holes made for plumb­ing and ser­vices — all of which leak air (and con­se­quently heat) if they aren’t sealed cor­rectly.

Car­ried out and cer­tifi­cated by li­censed testers, an in­flat­able door with an elec­tric fan in it is fit­ted to an ex­ter­nal door­way. Sealed air­tight, the fan blows in ( cre­at­ing pos­i­tive pres­sure) or sucks out (cre­at­ing neg­a­tive pres­sure) to achieve a pres sure dif­fer­ence be­tween the in­ter­nal and ex­ter­nal air of 50mb. (Be­cause of this, the test can’t be done on windy days when the air pres­sure out­side is un­sta­ble.) Wired to a lap­top the pres­sure sen­sor mea­sures the loss (or gain) of pres­sure over a pe­riod of time and hence records the air leak­age rate from the house. The speed at which it loses its in­ter­nal air is the fig­ure then in­serted into the SAP cal­cu­la­tions to work out whether com­pli­ance has still been met.

With the real air leak­age rate known and a cer­tifi­cate is­sued, the fig­ure can be en­tered into the as- built SAP cal­cu­la­tions. Th­ese fig­ures are then run again to pro­duce ev­i­dence of com­pli­ance and the fi­nal EPC.

If the house fails due to air leak­age, the test en­gi­neers may use coloured smoke and pos­i­tive air pres­sure to re­veal where the gaps are. If it fails due to a change of de­sign dur­ing the build – per­haps a boiler was changed for a less ef­fi­cient one or the glaz­ing ar­eas were in­creased – the re­me­di­a­tion may be harder to achieve and may re­sult in the need for some so­lar-power in­stal­la­tion or heat re­cov­ery ven­ti­la­tion. (armed with heat re­cov­ery to steal back the heat from stale air be­fore it’s ex­hausted out, th­ese sys­tems

can be­come es­sen­tial in achiev­ing com­pli­ance.)

En­ergy Per­for­mance Cer­tifi­cates (EPC)

The EPC sum­marises the en­ergy ef­fi­ciency of your home us­ing a slid­ing/rat­ing scale. The scale is colour coded and al­pha­be­tised, run­ning from A to G: A (dark green) is highly ef­fi­cient; G (red) is low ef­fi­ciency. New build homes to­day mainly fall in A or B cat­e­gories. Once your new home is com­plete, a full EPC and rec­om­men­da­tion re­port will be needed for present and fu­ture own­ers. And, as al­ways, your build­ing con­trol bod­ies should be sent a copy.

One of the most crit­i­cised fea­tures of EPCS is the fi­nan­cial as­sess­ment of how much money it will cost to run the house. This is not sur­pris­ing, given that it quotes pre­cise fig­ures which rarely turn out to be any­thing close to ac­cu­rate in real life. I don’t per­son­ally see this fea­ture as help­ful be­cause it’s based on stan­dard­ised as­sump­tions rather than re­al­ity such the num­ber of oc­cu­pants, hot wa­ter us­age, etc. The EPC costs ac­count for en­ergy used for heat­ing, light­ing and hot wa­ter, but do not in­clude other en­ergy uses in the home like cook­ing or elec­tri­cal ap­pli­ances, and th­ese fac­tors vary ap­pre­cia­bly be­tween dif­fer­ent house­holds and, of course, the de­gree of en­vi­ron­men­tal ex­po­sure to things like north winds make a huge dif­fer­ence to heat­ing.

So my ad­vice is to ig­nore this fig­ure. Like the band rat­ing, the cost fig­ure is just an­other way of com­par­ing homes on the mar­ket.

An EPC also takes into ac­count the price of the fuel used (per kwh) as well as the ef­fi­ciency of the heat­ing sys­tem. Elec­tric­ity is much more ex­pen­sive per unit than mains gas, which is one of the cheap­est forms of fuel. For ex­am­ple, if a home has a mains gas boiler, it will cost less to run than an elec­tric boiler or elec­tric stor­age heaters. The En­ergy Ef­fi­ciency col­umn in­forms the con­sumer about the heat­ing sys­tem purely from a cost per­spec­tive. The rat­ings in the ta­ble will vary de­pend­ing on the fuel used and the ef­fi­ciency of the heat­ing sys­tem. Even though an elec­tric heat­ing sys­tem may be 100% ef­fi­cient at the point of use, turn­ing all the elec­tric­ity used into use­ful heat, it will still be more ex­pen­sive to run than a 65% ef­fi­cient mains gas boiler. This is some­thing to con­sider if you are con­sid­er­ing un­der­floor heat­ing choices.

EPCS come with a rec­om­men­da­tion re­port with sug­gested im­prove­ments to save money and en­ergy. In the case of new build homes this bit is much shorter, with sug­gested im­prove­ments such as so­lar pan­els.

If you are sell­ing a home be­fore it has been com­pletely built, bear in mind that you will need to pro­vide in­for­ma­tion about en­ergy ef­fi­ciency done in the Pre­dicted En­ergy As­sess­ment (PEA) car­ried out at the de­sign stage.

An En­ergy-ef­fi­cient Build This self-build in Sh­effield, de­signed by Paul Testa Ar­chi­tec­ture, was rated a B un­der SAP cal­cu­la­tions, in line with around 80% of all new builds in Eng­land and Wales.

Try­ing to achieve ex­tremely low air leak­age rates of 1 or 2 comes with its own prob­lems. We are car­bon-based life-forms and we need to breathe air, so liv­ing in a her­met­i­cally sealed box is not ex­actly healthy for us, es­pe­cially when you con­sider the high lev­els of in­door air pol­lu­tion from clean­ing chemicals and fire-re­tar­dant fur­nish­ings, but mostly when you con­sider our com­bus­tion ap­pli­ances for heat­ing and cook­ing. Open flued or flue-less ap­pli­ances like log burn­ers and cook­ers can be­come lethal in air­tight build­ings where they are starved of oxy­gen. Ex­tra mea­sures, such as trickle vents, are needed for new build homes be­cause of their in­her­ent air­tight­ness, and some­times what be­comes nec­es­sary is a whole build­ing ven­ti­la­tion sys­tem that pro­vides back­ground air me­chan­i­cally (see page 117 for more de­tails).

Next month: Part H — Con­nect­ing to and build­ing near mains drains

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