Passivhaus PhPP help

[Nic]

hindsight is a wonderful thing ... however I need to move forward... sorry in advance for the long request 

 

I have an architect I really like and have submitted a design for an ICF, with raft, low energy build. The site I have did have planning for a small dwelling which was already approved ( another architect conventional build ) but due the changes I made it was thought best to pop in another application. That has been with planning now for a month , so far no objets , fingers crossed. The footprint of the building is a box shape ( no fancy details) only 94m2 and has a single mono slope roof at about 5 degrees.

The plans submitted have kept the sw and se windows relitively small The corner of the property is on the south axis .

I now am thinking I should just go fully for the Passivhaus certification.

 

So I see I have these options if I choose to go down that route

1. find a new architect that is PHPP and start again ( not ideal )

2. ask if there are any PHPP consultants who are prepared to just work with my architect  ( in principle am I then paying almost twice for the same thing? ) 

3. Is it possible to ask someone who has knowledge of the PHPP software to look at the design and plug in the basics of what I have to see how far off the design is and discuss options there?

4. can you ask someone to do all the PHPP ( who may not be officailly accredited ) to then just have an accredited PHPP done at the end and then either pass or fail ( but know you are very close to passive having worked mainly with the PHPP all the way through the build ....

 

 

yes I know and apology's in advance.... really not sure best course of action  and of course budget is tight as it always is with these things 

[IanR]

5 minutes ago, Nic said:

1. find a new architect that is PHPP and start again ( not ideal )

2. ask if there are any PHPP consultants who are prepared to just work with my architect  ( in principle am I then paying almost twice for the same thing? ) 

3. Is it possible to ask someone who has knowledge of the PHPP software to look at the design and plug in the basics of what I have to see how far off the design is and discuss options there?

4. can you ask someone to do all the PHPP ( who may not be officially accredited ) to then just have an accredited PHPP done at the end and then either pass or fail ( but know you are very close to passive having worked mainly with the PHPP all the way through the build ....

2. Someone like: Dr. Rod Williams of Williams Energy Design

https://passivehouse-international.org/memberSearchDetails.php?member_id=2349

No overlap with your Architect, Rod would do the thermal modelling and suggest/recommend improvements to you/your Architect.  If you have some inherent design issues, say cold bridging at door thresholds, you'll need to decide who re-designs this area, who has the expertise in your chosen build method.

3. Full detail is required unfortunately. There's not a short cut.

4. Then you paying for it twice, and hoping you meet targets with a guestimate.

[Nick Laslett]

You can achieve near Passivhaus like levels in a build without going through the whole process. 
 

For walls, windows, foundation, roof and airtightness you can spec passivhaus levels of materials. The successful implementation of all this is what is key. Neither your architect or PHPP consultant will really be much help there. 
 

If you have gone for passivhaus levels of insulation, the other area that might need some attention is overheating in the summer from solar gain. This is why most passivhaus designs have overhangs for the south and west facing windows. 
 

As @IanR says, there are no short cuts to actual Passivhaus certification. 

Edited November 27, 2023 by Nick Laslett

[Alan Ambrose]

>>> I now am thinking I should just go fully for the Passivhaus certification.

 

You don't say why? You can do the calcs yourself if you are happy with uncertified. Or if it's just insulation modelling, Mr Harris' spreadsheet.

[Nic]

Thanks main reason is to make sure I get it right as it’s all new 

 

where can I find mr Harris’ spreadsheet ?

 

thanks

 

 

 

[IanR]

11 minutes ago, Nic said:

where can I find mr Harris’ spreadsheet ?

 

Edited November 27, 2023 by IanR

[Iceverge]

Welcome welcome. I do like small houses. 

 

 

You could post a few of your plans here (deidentified)  and I could have a gander. I did my own PHPP and it isn't too tricky really for simple house. Jeremy's Harris's spreadsheet is probably just as useful in reality. 

Passivhaus isn't a perfect standard however and it favours larger buildings. Small single story houses can be tricky to meet the standards as they have lots of surface area Vs their volume. 

 

Have a look at these examples. 

 

https://passivehouse-database.org/index.php?lang=en#d_6778

https://passivehouse-database.org/index.php?lang=en#d_5132

https://passivehouse-database.org/index.php?lang=en#d_2096

https://passivehouse-database.org/index.php?lang=en#d_4466

 

You'll note that they often need extremely low U-Values for certification. Far below 0.1W/m2K in many cases. No problem in that itself ( I'm all for insulation) but it may not be needed for passivhaus performance.

 

The problem is better explored here. 

 

The small passive house problem - a solution? - passivehouseplus.ie

 

 

 

The passivhaus 10W/m2/annum was designed around forgoing a central heating system so is rather arbitrary, much like the 20deg living temperature and the assumed occupation rates. 

 

It's an excellent standard and I'm a total advocate of the methodology but don't tie yourself to certification without being informed of it's drawbacks. 

 

 

[Dan F]

1 hour ago, Nic said:

Thanks main reason is to make sure I get it right as it’s all new 

 

If you can afford it, it's a good idea to get someone to do the modelling before you build.   This allows you to adjust window sizes, overhangs and shading to get things to a place where you are happy with sizes and overheating risks.  If you don't do this then yes,  i) your windows might be smaller than they needed to be, or you might need to retrofit shading after the fact which is less than ideal etc.   This same modelling will give you an idea of what your heating costs will be given your chosen level of insulation as well as if active cooling may be required/desirable.  For this exercise to be worth doing and for you to be confident in the results, then it needs to be done properly, ideally by someone who has experience and done it before.

 

Then, once you are ready to build it is a separate decision you need to take in terms of certification. At this point, you've already got the value out of the modelling and the reasons to certify would be i) the certification itself (minimal value unless it's important to you) ii) the fact it enforces more rigour and quality control and so, the final build should be closer to what was modelled.  That said if you are very hands-on and have the knowledge/experience you could achieve the same level of quality without certifying.  The certification isn't the only way to achieve quality, but it's a good way if you are new to the game.  For example, as part of the initial modelling thermal bridges weren't analyzed, but because we were planning to certify more effort went into ensuring thermal bridges were correct (between PH designer and MBC) than would have happened otherwise.

 

Edited November 27, 2023 by Dan F

[Iceverge]

@Nic

 

Has sent me a PM and I've replied. I'd encourage you to post publicly as people can check my workings and hit me over the head with a metaphorical mallet I'm spouting nonsense. 

 

 

 

 

[Nic]

@iceverge 

 

kindly looked at this for me and replied as below. As they said any other comments are welcome.. 

the two add on ‘pods ‘ as I call them are because I will never be granted a bigger overall house from planning but they may allow the little extra single story ‘pods’ which would help.  So here is the message . Which I’m very grateful for. This forum is invaluable I’ve learnt so much from my posts . Thanks to everyone 

Nic 

 

 

Here we go. 

 

I've thrown about an hour at this drawing. Its like a cardboard cut out  template of a house  

 

PHPP uses external dimensions unlike SAP. 

 

NE wall 46.7m2 Window 3.3m2

NW wall 51.7m2 Window 14.5m2

SW wall 46.1m2 Window 4m2

SE Wall 61.9m2 Window 12.3m2

Floor 94m2

Roof 94.6m2

 

Your current wall thickness is 400mm. Roof is 350mm. 

 

This would result in U values of about 0.16W/m2K with ICF and a  joisted roof. Lets assume you can install a floor as thick as you wish with a U value of 0.1. Windows at 1.1w/m2k installed. 

 

I note you're in the south coast. Lets assume zero as a minimum temperature. A good airtightness score and MVHR. Take any internal heat gains to be cancelled out by minor thermal bridging and the inefficacy of the MVHR. That leaves us a simple enough sum to do. 

 

Area X U value X delta T = Heat Loss Total

 

Your heating load as stands would 

 

Roof: 94.6x0.16x20= 302w

Floor 94 X 0.1 X 15 = 141w

Walls 206.4 x 0.16 x20 = 660w 

Windows 34.1 x 1.1 x 20 = 750.2 W

 

Total heating demand 1853 w. 

 

The foot print is 94m2 and the floor area is about 150m2. 

You're at roughly 12.5W/m2K specific heat demand vs the Passivhaus limit of 10W/m2K. 

 

 

There's a couple of things you could do to adjust. 

 

The small add ons to the south and west adddisproportionately more external surface area than the floor area. For instance the one to the west adds only 5.5m2 of floor area but 131W of heat load or 24W/m2. It's twice as bad as the average of the house. Designing from scratch they'd be a far more expensive option than just making a house a pure 4 sided box or even a full height "T" or "L".  I understand you are size limited but slightly thicker walls or roof would help. Only marginally. 

 

As you can see even good triple glazed windows loose a tremendous amount of heat. More than all the walls combined. You have 14m2 of windows on the North wall. This will loose heat all year around as unlike the South facing window's they'll never gather energy. ( Nett loss) Consider making them smaller. For mainly this reason it's very unlightly you'll be near the annual heat demand of a passivhaus. I would guess you'll be about 4000kWh per year. Assuming a well functioning ASHPand 25p/unit this will translate to about £250/year for space heating.  A passivhaus might be £150. 
 

 

Over all, if built to good standards of airtightness and thermal bridging you'll have a very warm house.  

 

 

 

 

 

[Alan Ambrose]

@Iceverge

 

Thanks for the very clear 'heat loss in a nutshell explanation'. Very useful for everyone, I think.

 

Love the colourful fold-up cardboard cutout version of the house design - was that used somewhere, or just to illustrate the surface area?

 

I just bought PHPP yesterday, so @Nic thanks for bringing this subject up at this time

 

 

[Iceverge]

Here's a suggested roof build up 

 

 

 

I've gone for a trapizoidal profile metal roof.

 

 

Far cheaper and less temperamental than standing seam etc. Also a thinner build-up. as you can effectively ventilate under the sheeting with 20*70mm  strapping as fixing battens. 

 

Then a good breather membrane. Taped at all joints of course. 

 

Then 11mm OSB, for rodent protection, solidity, noise, ease of buildability. 

 

220mm rafters ( if ok with the SE) with densepack cellulose insulation. Great for noise, airtightness, decrement delay etc.

 

A Vapour control layer. 

 

A 44*70 mm crossbattened service cavity with mineral wool insulation.  It would be enough to accommodate flat uPVC MVHR ducting if needed. If you pushed this to a 88mm or 95mm service cavity you could run semi rigid MVHR ducting no problem. 

 

If you could a second layer of standard plasterboard or a single layer of 15mm PB would help with noise. 

 

 

 

 

 

NIC roof buildup.pdf

[Alan Ambrose]

Mineral wool in the service void as it's more practical to install there than cellulose?

 

Any utility in using posi joists rather than standard rafters so you could run MVHR ducting there?

 

Can I ask how you chose 1.4 as a target u-value? Is that a typical optimum value in practice?

Edited November 28, 2023 by Alan Ambrose

[Russdl]

@Nic A quick comment on the current design, your low pitched roof is facing northwest so not ideal for solar if you were planning on that.
 

Can you slope it south east, that would be much more favourable for PV production and then you could start looking at Passive Plus or more. 

[Nic]

Can’t change the roof aloof as not allowed larger visible mass on the NW side which is of course what o would have preferred for the reasons you mentioned 

[Iceverge]

3 hours ago, Alan Ambrose said:

Mineral wool in the service void as it's more practical to install there than cellulose?

 

Any utility in using posi joists rather than standard rafters so you could run MVHR ducting there?

 

Can I ask how you chose 1.4 as a target u-value? Is that a typical optimum value in practice?

 

You could put cellulose in the service void too but it'd mean cutting holes in the plasterboard to blow it in and a second visit for the installer truck. The main benefits would be already had in the main 220mm depth of the rafters. Namely, decrement delay (phase shift, airtightness enhancement and the ease of install around awkward cuts of timber etc. ( Not a huge factor in this roof) 

 

Mineral wool is cheap and if you correctly space the counter battens for the service void can be very quickly fitted. 

 

As @Nic mentioned budget I am conscious that posi joists are probably 5 times the price of cut lumber and a special order item rather than an off the shelf thing from a merchants. Beware 220mm timber rafters will need intermediate support. 

 

Re the U-Value of 0.14. It's just what emerged given the space constraints.  

 

The OP is limited in their height build-up to 350mm.  Trade off's need to be had between the cost of materials and performance. A 400mm I beam with cellulose and woodfiber sheathing would be ace but probably 3 times the cost. 

 

Similarly PIR between the rafters with PIR underneath would appear cheaper and have a lower U value. 

 

 

 

However it's very tricky to install the PIR accurately. Differential movement of the timbers and PIR over time will result in gaps and thermal bypass of the insulation. There'll be loads of waste from the PIR boards cuttings. It has a worse decrement delay resulting in poorer summer performance. It'll be much much worse from a noise and airtightness perspective. 

 

 

 

[Nic]

4 hours ago, Iceverge said:

Here's a suggested roof build up 

 

 

 

I've gone for a trapizoidal profile metal roof.

 

 

Far cheaper and less temperamental than standing seam etc. Also a thinner build-up. as you can effectively ventilate under the sheeting with 20*70mm  strapping as fixing battens. 

 

Then a good breather membrane. Taped at all joints of course. 

 

Then 11mm OSB, for rodent protection, solidity, noise, ease of buildability. 

 

220mm rafters ( if ok with the SE) with densepack cellulose insulation. Great for noise, airtightness, decrement delay etc.

 

A Vapour control layer. 

 

A 44*70 mm crossbattened service cavity with mineral wool insulation.  It would be enough to accommodate flat uPVC MVHR ducting if needed. If you pushed this to a 88mm or 95mm service cavity you could run semi rigid MVHR ducting no problem. 

 

If you could a second layer of standard plasterboard or a single layer of 15mm PB would help with noise. 

 

 

thanks once again 

 

How are Solar connected through the roof sheet? I know on the standing seam style they have an external clamp that attaches to the seams 

 

 

 

4 hours ago, Iceverge said:

 

 

 

NIC roof buildup.pdf 1007.31 kB · 4 downloads

 

[Iceverge]

27 minutes ago, Russdl said:

@Nic A quick comment on the current design, your low pitched roof is facing northwest so not ideal for solar if you were planning on that.
 

Can you slope it south east, that would be much more favourable for PV production and then you could start looking at Passive Plus or more. 

 

Good thinking. It makes a difference but not as much as you'd thing at very low pitch angles. Here's the north facing one from PVGIS. 

 

 

Here's the South . 

 

 

The difference is only about 300kWh/year. It'd be easily compensated for by adding a single extra solar panel. 

 

@Nic I would consider moving all the PV to the roof in one block. Less lightly to suffer differential shading which I gather it doesn't like unless you have some clever inverter gizmos. Some PV guru's could probably enlighten me.  

 

 

 

 

[Alan Ambrose]

>>> Some PV guru's could probably enlighten me.  

 

Hardly a guru, but each PV panel string usually sits on one central inverter input (or MPPT) and will be limited to the output current of the lowest panel - the panels are literally strung together in series. A string is usually limited up to, say, a dozen panels and is limited to the max inverter input voltage. Total voltage is approx. # panels x 40V. So shading one panel will reduce the output of all the panels to the same extent.

 

With local inverters, there's usually one inverter for each panel (they sit on the roof too) and there's no such limitation. Of course, this option is usually more expensive.

[Nic]

14 minutes ago, Iceverge said:

 

Good thinking. It makes a difference but not as much as you'd thing at very low pitch angles. Here's the north facing one from PVGIS. 

 

 

Here's the South . 

 

 

The difference is only about 300kWh/year. It'd be easily compensated for by adding a single extra solar panel. 

 

@Nic I would consider moving all the PV to the roof in one block. Less lightly to suffer differential shading which I gather it doesn't like unless you have some clever inverter gizmos. Some PV guru's could probably enlighten me.  

 

 

 

 

Can’t change the roof slope as not allowed a larger visible mass on the NW side !! which is of course what I would have preferred for the reasons mentioned 

 

[Nic]

On 28/11/2023 at 11:11, Iceverge said:

Here's a suggested roof build up 

 

 

 

I've gone for a trapizoidal profile metal roof.

 

 

Far cheaper and less temperamental than standing seam etc. Also a thinner build-up. as you can effectively ventilate under the sheeting with 20*70mm  strapping as fixing battens. 

 

Then a good breather membrane. Taped at all joints of course. 

 

Then 11mm OSB, for rodent protection, solidity, noise, ease of buildability. 

 

220mm rafters ( if ok with the SE) with densepack cellulose insulation. Great for noise, airtightness, decrement delay etc.

 

A Vapour control layer. 

 

A 44*70 mm crossbattened service cavity with mineral wool insulation.  It would be enough to accommodate flat uPVC MVHR ducting if needed. If you pushed this to a 88mm or 95mm service cavity you could run semi rigid MVHR ducting no problem. 

 

If you could a second layer of standard plasterboard or a single layer of 15mm PB would help with noise. 

 

 

 

 

 

NIC roof buildup.pdf 1007.31 kB · 9 downloads

 

 

 

can anyone recommend a good roofer in the Exmouth area?