What is En­erPHit?

While Pas­sivhaus is, for many, the go-to stan­dard for low-en­ergy new builds, ar­chi­tect Paul Testa ex­plains how En­erPHit, the equiv­a­lent for ex­ist­ing prop­er­ties, could ben­e­fit ren­o­va­tors look­ing to im­prove the en­ergy ef­fi­ciency of their home

Homebuilding & Renovating - - CONTENTS -

Many of us are fa­mil­iar with the term Pas­sivhaus — per­haps the ul­ti­mate low-en­ergy stan­dard for new builds. But did you know there was an equiv­a­lent for ex­ist­ing homes? Ar­chi­tect Paul Testa, who is em­bark­ing on his own En­erPHit project, ex­plains all

Many peo­ple love their ex­ist­ing home for a num­ber of rea­sons – the lo­ca­tion and the neigh­bours, for in­stance – but are of­ten faced with a dilemma when the house fails to meet cer­tain re­quire­ments. These could in­clude space and de­sign but also com­fort and per­for­mance. Do you move, or im­prove? Like­wise, there are those who want to build their own home in or­der to have a greater in­flu­ence over these el­e­ments, but strug­gle to find a new build plot (my­self in­cluded!).

This is when we might be­gin to think about tak­ing on a ren­o­va­tion, re­model and/or ex­ten­sion project. While this type of project can cer­tainly de­liver more space, what about com­fort and ther­mal per­for­mance?

Step in retro­fit. Retro­fit is a form of ren­o­va­tion, typ­i­cally un­der­taken to greatly re­duce en­ergy con­sump­tion. As such, retro­fit in­volves a sig­nif­i­cant im­prove­ment in the ther­mal per­for­mance and com­fort of your home. More specif­i­cally, it is about im­prov­ing the build­ing fab­ric rather than sim­ply the in­tro­duc­tion of re­new­ables.

The chal­lenge is that it is dif­fi­cult to know how far to go and pre­dict how much com­fort and per­for­mance your retro­fit mea­sures will de­liver. To this end, you need some­thing to mea­sure against and com­pare per­for­mance with known bench­marks. The Pas­sivhaus stan­dard is per­haps the best known of the en­ergy ef­fi­ciency fab­ric stan­dards for new builds, and the good news is that this stan­dard has been adapted for ex­ist­ing homes, too. Ap­ply­ing spe­cific Pas­sivhaus prin­ci­ples to an ex­ist­ing prop­erty on a retro­fit ba­sis can re­sult in a high per­form­ing home — and this is where En­erPHit comes in.

What is En­ErPhit?

Un­like a new home built to Pas­sivhaus stan­dard, when you’re con­sid­er­ing a retro­fit, many of the el­e­ments like ge­om­e­try, ori­en­ta­tion and struc­tural ap­proach are al­ready de­cided be­cause we’re work­ing with an ex­ist­ing build­ing. You may also have ther­mal bridges (or cold bridges: a path for heat to es­cape through gaps in in­su­la­tion) that are dif­fi­cult to com­pletely elim­i­nate.

The En­erPHit stan­dard recog­nises this dif­fi­culty and sets the re­quired per­for­mance at a lower level than Pas­sivhaus to ac­com­mo­date work­ing with ex­ist­ing build­ings.

To achieve En­erPHit you must achieve a space heat­ing and cool­ing de­mand of 25kWh/m2/year (com­pared to the Pas­sivhaus stan­dard of 15kWh/m2/ year) and in­stead of an air­tight­ness per­for­mance of 0.6 air changes per hour you need to achieve 1.0 (the Build­ing

More than 85% of the homes that will ex­ist in 2050 are al­ready built, and a huge per­cent­age of our en­ergy us­age and car­bon emis­sions comes from our homes. If we’re go­ing to meet our 2050 car­bon re­duc­tion tar­gets, then retrofitting ex­ist­ing prop­er­ties is go­ing to play an im­por­tant part.

Regs for new homes re­quire be­tween 5 and 15 ac­cord­ing to the Char­tered In­sti­tu­tion of Build­ing Ser­vices En­gi­neers). We’re talk­ing about the same Pas­sivhaus com­fort but util­is­ing slightly more en­ergy. It is still a huge im­prove­ment on most ex­ist­ing homes and even new builds.

En­erPHit of­fers a bench­mark for ren­o­va­tors to work to. Like Pas­sivhaus, we use the Pas­sivhaus Plan­ning Pack­age (PHPP) de­sign tool (see be­low left for more) when de­sign­ing an En­erPHit scheme. This helps us to de­liver more ef­fi­cient build­ings at an early de­sign stage, con­sid­er­ing ori­en­ta­tion and ge­om­e­try. The PHPP also al­lows us to make in­formed de­ci­sions about where to spend money and to un­der­stand what cost and en­ergy im­pli­ca­tions there are in var­i­ous retro­fit mea­sures and the al­ter­na­tives that might be be­ing con­sid­ered.

Retrofitting is not easy, how­ever, and En­erPHit is a tough stan­dard to achieve; the ther­mal and air­tight­ness strate­gies are likely to be more com­plex and more dif­fi­cult on site than with a new build. You may have to bal­ance the pros and cons of in­ter­nal or ex­ter­nal in­su­la­tion, and po­ten­tial mois­ture is­sues that come from chang­ing the build­ing fab­ric. More so than ever, it de­mands a skilled and in­formed de­sign team.

That said, per­haps the ul­ti­mate ben­e­fit of aim­ing for the En­erPHit stan­dard and for full cer­ti­fi­ca­tion is the rigour and qual­ity as­sur­ance it de­mands. Fol­low­ing the cri­te­ria en­sures that the works are com­pleted in the way they are de­signed; that the air­tight­ness per­for­mance is achieved and that there are no fudges along the way.

Anec­do­tally, from talk­ing to other ar­chi­tects and con­sul­tants, hav­ing a de­fined cer­ti­fi­ca­tion stan­dard to achieve ac­tu­ally makes it an eas­ier team ef­fort; there’s no ac­cept­ing a slight slip in per­for­mance and the whole team has a shared goal.

What’s in­volvEd

When car­ry­ing out an En­erPHit, there will be a list of mea­sures re­quired in or­der to meet the stan­dard. These will in­volve:

• High lev­els of in­su­la­tion — either in­ter­nal or ex­ter­nal, although in­ter­nal needs more care in terms of mois­ture risk.

• High per­for­mance triple-glazed win­dows and ex­ter­nal doors.

• Care­ful con­sid­er­a­tion of win­dow in­stal­la­tion.

• An air­tight­ness read­ing of 1.0.

• A me­chan­i­cal ven­ti­la­tion with heat re­cov­ery (MVHR) sys­tem.

As the stan­dard you’re work­ing to is a recog­nised bench­mark, in or­der to re­ceive En­erPHit cer­ti­fi­ca­tion, the process is ex­actly the same as work­ing to­wards Pas­sivhaus cer­ti­fi­ca­tion. In or­der to meet these re­quire­ments, the project must be de­signed us­ing the PHPP and must be cer­ti­fied by

an ac­cred­ited Pas­sivhaus cer­ti­fier. Although the prod­ucts you’re in­clud­ing within the house do not need to be cer­ti­fied for Pas­sivhaus, it does help, es­pe­cially with MVHR equip­ment.

The cost of an En­erPHit retro­fit, how­ever, will vary, as the more com­plex an ex­ist­ing house is the more com­plex the retro­fit will be. How­ever, I’d rec­om­mend bud­get­ing around £800-£1,000/ m2 for deep retro­fit/En­erPHit — plus the VAT as you’re deal­ing with an ex­ist­ing build­ing. For typ­i­cal com­po­nent or sys­tem costs, how­ever, you can ex­pect to pay around £10,000 for a MVHR unit in­stalled in an av­er­age-sized house, and ap­prox £400-£600/m2 for win­dows and doors. The big costs, though, are in labour — the in­stal­la­tion of the in­su­la­tion and air­tight­ness mea­sures is time­con­sum­ing and needs to be done with care.

WhEn to takE thE lEaP

An En­erPHit retro­fit makes most sense when you’re al­ready con­sid­er­ing ren­o­va­tion or re­mod­elling work to your house. In my opin­ion, why not go the ex­tra mile when you’re un­der­tak­ing works any­way? Why not make the ad­di­tional in­vest­ment in time and ma­te­ri­als to achieve much bet­ter per­for­mance and bet­ter com­fort for your­self and your fam­ily when there’s works be­ing car­ried out to your home al­ready? Par­tic­u­larly in cases where you’re look­ing to make changes to your home and al­ready con­sid­er­ing im­prov­ing its en­ergy ef­fi­ciency, En­erPHit makes per­fect sense.

The eco­nomic ar­gu­ment for im­prov­ing the per­for­mance of the roof when it needs re­plac­ing, or in­stalling triple glaz­ing rather than dou­ble-glazed win­dows when they need chang­ing, is a much eas­ier one to jus­tify and of­ten the num­bers stack up. The key thing is to have a whole house plan from the be­gin­ning so that each mea­sure works to­gether in the long-term, giv­ing you the end re­sult of a high per­form­ing home. If you’re con­sid­er­ing an ex­ten­sion, this may not be the time for you to un­der­take a retro­fit, but it’s a great time to make a long-term whole house plan that en­sures the ex­ten­sion works as an in­te­gral part of that strat­egy; it would be frus­trat­ing to find that your ex­pen­sive and beau­ti­ful ex­ten­sion has cre­ated a bar­rier to a more in-depth retro­fit in a few years’ time.

So if you’re con­sid­er­ing ren­o­va­tion or re­pair works to your home with a view to achiev­ing high lev­els of com­fort and ther­mal per­for­mance, then now could be the time to plan for an En­erPHit retro­fit. H

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