Totnes Passivhaus B&B

Transcription

1 Totnes Passivhaus B&B Case Study Passivhaus retrofit lessons learnt living experience Bristol European Green Capital Passivhaus Conference 17 November 2015, Bristol Living in a Passivhaus Lessons learnt from one of the country s first Passivhaus projects Adam Dadeby Passivhaus Homes Ltd. 1

2 Living in a Passivhaus Lessons learnt from one of the country s first Passivhaus projects Background to project - why we chose Passivhaus How we set about it How we assembled the team Design process The Build Costs Living in the Totnes Passivhaus 2

3 A low net energy future Our task for the next 100 years is simply to get off fossil fuels, nothing more, nothing less. If we don t do that, nothing much else will matter because we probably won t survive. We need to undertake [the energy] transition carefully, intelligently [and] co-operatively Richard Heinberg, Totnes Civic Hall, 22 Nov

4 Background to Totnes Passivhaus Private home and B&B! Very limited choice of plots/properties Our brief Ultra low energy use Future-proof for autonomy Invest now to save Minimise technology Comfort! Personal journey: peak oil moment CAT AEES CEPH PH designer course Passivhaus Handbook Passivhaus Homes/Store Estate has strong modernist style, locally architecturally significant Existing building was in urgent need of extensive & expensive repairs! 4

5 Project timeline Apr 09 May Jun 09 Oct 09 Apr 10 Feb 10 Apr 10 Jul Oct-10 8-Nov-10 5-Apr Jul Aug-11 Sept 2011 Project initiation, pre-planning enquiries Architect selection Detailed design and PHPP modelling Contractor selection Submission of planning application Re-design following change of heart by planners Planning permission granted Construction commences First air-tightness test: result 0.4 ach Certification air-tightness test: result 0.2 ach Move back into house Passivhaus Certification design build 5

6 Lessons: choice of building/site Criteria Minimise planning constraints Ideal Not listed building Not in a conservation/ architecturally sensitive area Met by our house? Yes Yes and no No/limited shading Un-shaded solar gain façades Partly Feasible to insulate the floor Available ceiling height or suspended floor External insulation feasible Solid walls, rendered finish, large roof overhang (unless it is being replaced) Partly Build quality Original structure built to a decent standard (hidden quality) No!! Form factor Efficient (low ratio of TFA to external envelope area) No* Climate Nice and mild! Yes Shading No significant shading Not really * until it was extended 6

7 Form factor impact of building shape - 1 Terrace or apartment block Bungalow Courtesy: WARM low energy building practice 7

8 Form factor impact of building shape - 2 Form factor is the ratio of external thermal envelope to treated floor area Form factor Typical type of dwelling this might represent < 2 Apartment block or terrace (row houses) 0.15W/m²k Wall/roof/floor approximate range of U-values needed to reach below 15 kwh/m2.a in the UK 2 to 3 Semi-detached or compact detached two or three storey property 0.10 to 0.15 W/m²k Totnes PH = to 4 Less compact detached house or bungalow 0.10 W/m²k > 4 Very spread out bungalow 0.05 to 0.10 W/m²k * Credit: Warm Low Energy Building Practice 8

9 Elevations existing and new 9

10 Choosing the architect and builder Passivhaus unlearning experience for architect & builder Trust, co-operation and Common Purpose essential Think of ways to involve contractor candidates early in the project Education consists mainly in what we have unlearned. Mark Twain, 1898 Contractor briefing/training - understand the what and why of Passivhaus In-house, multidisciplinary contractor team vs. many sub-contractors Culture change to: Avoid blame game Unlearn old habits Common Purpose is a shared intention to achieve a shared goal, where collective aims are advanced by the individual purpose, and individual aims are advanced by the collective purpose. David Fleming, 2010, from Lean Logic 10

11 Planning particular challenges of a Passivhaus retrofit More design work undertaken before planning permission granted particularly on a first PH project, particularly if it is retrofit how many clients are willing to spend significantly at risk? Extra spend before PP added to planning stress more at stake. All the benefits of ultra low energy building set out in planning application, but in practice has very little traction in promoting the application. Will PH have more credibility with planners as sustainability standard in the future? Shading requirements challenge UK s vernacular traditions 11

12 Costs Totnes Passivhaus is about double the size of the average UK home Build cost 330k ex VAT, professional fees about 40k Treated floor area (TFA) PH floor measuring convention: 162m² SAP net internal 185m² Gross floor area 236m² - cost per gross floor m²: 1400 cost per net (SAP) m² floor area: 1785 thicker walls in a PH mean bigger per m² cost difference between net and gross floor measurement conventions However figures include: large solar thermal array three high-end bath/shower rooms handmade kitchen extra costs to repair existing fabric Estimated that extra cost of PH in this project 40k to 50k early adopter premium + retrofit complexity That said, current estimated value of the property more or less in line with total spend, including purchase of original house. Did planning add more costs than Passivhaus?

13 PH or not, what factors impact on cost? Acquiring suitable building land England has massive concentration of ownership, land banking we need a Land Value Tax! Site access bringing all materials to site in a transit van costs Site gradient every 5 of slope adds 50/m² of floor area Demolition costs add 5 to 10k, or more if difficult site or materials (asbestos) Retrofitting 20% VAT on construction costs, VAT free on new builds Retrofitting much bigger contingency needed inherently complex and risky Services water, sewage, electricity, telecoms, gas grid or off-grid. Planning constraints period windows, stone finishes and any one of a 100 other stipulations by the planners Changing the project brief or scope clients beware! Not making (timely) decisions clients beware! The state of the economy demand for builders & architects Trust and co-operation between client, builder & architect 13

14 What design factors help to save money? Spend more time on design and less on build Compact form (good form factor) Simple shape (no fiddly bits) Moderate quantity of glazing (glazing area, number of windows, window type) Windows not too big, not too small Efficient building method Moderate floor area (how much space do you need?) The cheapest often defers expense rather than saves it. New builds simpler than retrofits/refurbs 14

15 Lessons learned 1. Not every property is suitable for PH/EnerPHit retrofit, but rigour of PH methodology can be applied, even if less demanding target energy standard chosen, e.g. AECB Silver. 2. Get the form factor right and your task becomes easier if existing building has a poor form factor, does the addition of an extension improve it? 3. Consider shading/overheating avoidance strategy before planning more imaginative/bespoke solutions may be needed in a retrofit. 4. Is the building really worth saving? Don t let sentiment or belief in retrofit determine choice. Critically assess risks & costs (incl. VAT), financially and energetically (embodied energy) there are many variables (obviously). 5. Need to make sure whole contractor/sub-contractor team understands why & how of all key concepts, specifically: airtightness, thermal bridging, ventilation, quality and reporting errors and problems. 6. Use the PHPP to try to avoid relying on the most high-spec components windows, insulation etc. not doing so narrows down options and may increase risks and costs. 7. MVHR ductwork use of semi-rigid, radial ducting particularly helpful in retrofits. 8. Choice of MVHR and other components growing should aid PH/EnerPHit projects. 9. Competitive tendering needs to be rethought as a way to test the market. 10. Retrofits likely to need THERM modelling and a lot more design input. 15

16 What is it like to live in the Totnes Passivhaus B&B? (impressions of the occupants and B&B guests) Comfort, comfort, comfort this is the enduring plus nearly every visit to a normal house underlines this! Very quiet airtightness and triple-glazing keep out traffic noise Warm in winter, very little overheating in summer Good air, noted by many of our guests We can open our windows for greater % of year MVHR v. quiet (no perceptible noise in bedrooms, barely audible in bathrooms & kitchen) great not to have noisy purge bathroom extracts Would we every go back to living in a normal house uh, no! Have we changed the way we live? Bedrooms warmer than some would like solution open window thinner duvets Linger longer at front door no gale blowing through house MVHR takes care of cooking smells and humidity without need for boosting or recirculating extractors Clothes and towels dry quickly, relative humidity always stays in the healthy range, ca. 35% 70% The house just takes care of you very little adjustment of thermostats etc. needed to maintain comfort. 16

17 Passivhaus Refurb blog Passivhaus Refurb - the diary of the Totnes Passivhaus

18 Published by Green Books As we move towards the 2016 zero carbon target in house building, Passivhaus construction looks like becoming not just popular in the UK, but commonplace. This is a no-nonsense and engaging introduction to how to do it. Kevin McCloud Janet Cotterell Adam Dadeby

19 Question time

20 Building stats Original structure built 1971, typical construction: dense concrete block cavity walls, concrete slab, concrete tiles Project doubled building size to TFA 162m², SAP 185m² Mixture of two building styles masonry and timber Windows, triple glazed and windows (with integral blinds) Internorm Varion/Varion 4 MVHR Paul Novus 300, 0.24Wh/m³, 93% HR efficiency Solar thermal 9.4m² drainback system, west facing Solar PV 3.99kWp, east facing, transformerless inverter Thermal DHW store 500 litres, stratified Air tightness certificate 0.2 ach@±50pa Space heating at circa 14 kwh/m² per annum 20

21 Floor to Wall Detail Existing THERM modelling needed in many retrofits Thermal bridge unavoidable.

22 Retrofit Window Detail - 1 Airtightness sequencing. Position in wall Wrapping of frame

23 Retrofit window detail

24 Some photos from the project

25 Retrofit Roof-wall junction

26 New build construction wall-roof detail Ventilated!!.

27 New build construction wall-floor detail Thermal continuity position of insulation Less efficient but load bearing insulation.

28 Continuous Foamglas structural pads under slab Alternating

29 Defining airtightness layer. 29

30 Airtightness retrofit details 30

31 350mm I-beams on glulam ridge beam note airtightness sequencing

32 Ridge beam airtightness

33 Passivhaus retrofit 33