Thorfun

thanks for the additional information on points 1, 2 and 3. the calculator does indeed allow custom values and I've changed the lamda value of the PIR and Mineral Wool Batts to reflect the chosen insulation (defaults are 0.023 and 0.038 respectively). if I'm reading this correct, the timber frame itself has a massive impact on the overall U-value of the wall! I would assume that increasing the thickness of the PIR would reduce the impact the timber frame has as there is more insulation reducing cold bridging? I read somewhere (apologies but I can't remember where!) that the timber cladding would add an amount of insulation even if it is outside of the ventilated cavity. is that not the case at all then?

thanks for the response. I'm not in a position to buy stuff at the moment and so I haven't asked the manufacturers yet but I will do so once I get to that stage. I'm really at the planning stage to see how much I can reduce my reliance on PIR. 1. corrected/uncorrected: ok, this makes sense. so I would use the 0.14W/m2K U-value in this instance? 2. I thought this was dew point as well. I'll ignore this for the time being then and wait until I get proper calculations from the manufacturers or architect. 3. this is what I thought and no airspace is required. I will stick with fully filling between the studs. other comments: 1. is this true if using something this http://www.protectmembranes.com/protect-vc-foil-ultra-insulating-avcl/p/12? or do you just mention it because I have just got a basic polythene layer in the example? my intention is to use something like the Protect VC foil VCL/Airtight membrane but I couldn't see a way to accommodate that in the u-value calculator. 2. I haven't a clue how to do that in this calculator!

Hi all, I've been going through an online U-Value calculator to try and figure out my external wall make-up to get an idea of what I need to get a U-value. I have a few questions on the output: my questions on the screenshot below are: 1. what is the U-value (uncorrected) and U-value (corrected) differences? i.e. what is corrected U-value and which one would the TF manufacturers use in their marketing materials. so would this be a 0.14W/m2K or a 0.15W/m2K external wall? 2. on the right there is an image of the make up of the wall with a cross denoting "DP" within the 40mm of PIR. can someone please explain what "DP" is and is it being in the PIR an issue? also, where should it ideally be? 3. I have specified 140mm of mineral wool/glass wool (e.g. Frametherm 35) on this calculation. my architect has said that you shouldn't fully fill the stud work and should leave an air gap between the PIR and the mineral wool. is that true? if so, why would you need that? as leaving an air gap will reduce the U-value. thanks in advance.

as @ProDave has alluded to above if you want to build for near to £1000/m2 (especially in the south of England) then it takes time. one of either quality or speed of build will have to give and from reading his blog it is definitely not quality that has suffered! remember the time, quality, cost triangle. you can only have 2 of those choices.

Thanks again. It’s good to know I’m slowly getting a handle on things. That is until I start looking into another aspect of self-building!

thanks @A_L . if i'm reading page 12 of that document correctly (thanks for it btw, I shall read it in more detail when I have the time!) it looks like using something like the TF200 which is a low-emissivity surface will increase the external surface resistance further still to 0.29m2K/W. correct?

If using timber cladding then I assume that an external membrane on a timber frame would be a ventilated cavity though, right? as you have the external OSB covered by the membrane with the silver facing outwards into a cavity that has batons and the timber cladding on top. as the cladding is not airtight I presume that's considered a ventilated cavity. by that rationale the only external unventilated cavity would be brick cladding? we are having timber cladding so if that's the case then the silvered membranes won't benefit us at all.

it does seem that the TF200 is a popular choice with the timber frame manufacturers and I'll probably end up going that way although I guess it depends on who I choose! it's good to know that there's probably not much difference between the lot of them. the foil may well block mobile signals but I also think the 300mm of cellulose might have an impact as well! so I think even without the foil you might suffer.

this is a very interesting subject for me. I'm in the process of getting quotes for a timber frame and each manufacturer seems to have a different take on the external membrane for the frame. a number seem to go for the Protect TF200 Thermo with some offering it as an upgrade over the stock membrane. another has offered the Proctor Reflectashield TF0.81. do all these do pretty much the same thing? if so, does it simply come down to the timber frame manufacturers personal choice (or product endorsement for higher profit margin). I'm finding it really hard to determine what the best is or how to easily compare all products. e.g. the TF200 says "Aged Thermal Resistance 0.77m2K/W, the Proctor says "claimed thermal performance of 0.81m2K/W". So I would assume the Proctor Reflectashield is better as it has the higher R-value, but what does Aged mean? and I couldn't see an R-value listed on the specs of the Novia stuff! so, how does one determine the best membrane to use?

Thanks @Temp . sounds like a risk I don’t want to take for a few tomatoes!

yeah, fair comment, I just thought BT might want to upgrade the master socket to one of their new ones that don't need filters attached to them is all.

I would have thought it is a new router and master socket for FTTC at least and if it's FTTP then there's definitely a new box to accept the fibre cable required, so a home visit is definitely required. not sure what your 4g coverage is like up there but you could get a 4g modem and an unlimited data plan to see you through until you can get your new connection.

morning all, firstly, sorry to hijack this thread but I have a similar question so thought if I post it here it might be useful for others. We are still awaiting planning approval and there's a greenhouse near where the new house will eventually go. the ground floor plans from the architect that were submitted as part of the planning show the greenhouse location and it states "existing green house to be demolished". with the current lockdown we are thinking of moving it from it's existing location and putting it elsewhere on the plot so we don't have to demolish it and can use it in the meantime to grow veg. so, my question is would moving the green house be considered starting work and make us liable for CIL?

Hi and welcome! I'm a newbie here too. ? I have previously looked at Control 4 but it seems it's not that prevalent on here as a search for it really does not yield any posts. On an aborted project a number of years ago I had a couple of quotes for home automation using Control 4. one of them specified Lutron lighting and the other Control 4 lighting and the prices were dramatically better in favour of the Control 4 lighting. I have also recently had a demo at a store for Control 4 and it seems that their lighting controller looks very good and so maybe you should consider control 4 lighting instead of Lutron if going for a control 4 system anyway. oh, also I believe the lighting systems for these products uses Cat 6 cabling rather than normal lighting cable. so if you're going to put normal lights in to start with it might be worth checking with Lutron/Control 4 installers and running cat 6 cable along side the normal lighting cable for future upgrades. just a thought.

can't you get a second hand twin unit static caravan? then you can sell it on again when done with it. might cost a bit more than £20k but you'll recoup a lot of that.

I heard from my architect that our planning officer is still working on his workload albeit from home. I also expect some form of completely understandable delay which I am totally ok with!

Thanks. I think our sustainability credentials should be up there, apart from the concrete basement that is! ?‍♂️

Yep. Makes perfect sense. I’ll make a mental note to check it when we get to that point in the build! Thanks.

thanks @PeterStarck for confirming that I did understand what was written! I've come to the conclusion that the company I spoke to that won't use Posi-joists as they've had bad experiences with deflection on them maybe didn't install them at the correct centres or didn't add strongbacks. either way, I'm convinced I'm happy to go with Posi-joists.

this is interesting as our decision date is fast approaching and I was thinking that coronavirus is a great excuse for the planning department to ask for an extension. I might ask the architect to speak to them to get a feel as to how they're running things at the moment. despite how frustrating a delay would be, I would fully understand it (and honestly am fully expecting it!) as I'm not completely without a heart.

our architect has mentioned that maybe we could think about entering in to awards once the build is finished. I assume from that that he's very happy with the design he came up with (as are we). fingers crossed the planning department like it and we can get it built. then we can think about awards but it's something we hadn't even considered until the architect mentioned it.

so I finished reading (or flicking through) those 2 docs @PeterStarck linked (the Steico one was really dry and a tough read) but from what I can gather deflection isn't an issue unless you're getting to the limits of the specified beam and so I-Joists could also have deflection issues as well as Posis. It also seems that reducing the centres will reduce the deflection (is that correct?) as it makes a stiffer floor. so if one company is offering posi-joists at 600mm centres and another at 400mm centres then the floor with the 400mm centres will bounce less. is that also a correct assumption? The posi-joist brochure also talks about Strongbacks to reduce deflection so these can be added (and from the reading should be over certain spans) to assist. in fact, assuming I understand it all correctly, using Strongbacks on Posi-Joists results in less deflection ( span * 0.003 ) than the I-Joists (stated deflection of span * 0.004). this means for a 4.5m span the deflection of Posi-Joists with Strongback results in a 13.5mm deflection whereas the I-Joists would be 18mm. again, this is all assuming I understand it correctly! all of which means I'm feeling better about not having a trampoline on the first floor if I use posi-joists. ?

probably not very helpful but I'd get the architect (assuming you're using one!) to see what they think. but I would probably look to put it as close to the purple line as possible so you've got at least some south facing garden although I presume that your access is from the south so some of that south facing garden would be a driveway and garage. it might be nice to face the house east to west though to take advantage of the views but, again, as close to the junction of the purple/yellow/red line as possible. but, I would definitely seek the advice of a professional. then again, I don't have the knowledge nor experience of some of those on here so hopefully someone more helpful will be along soon. ?

we're awaiting planning permission at the moment (decision due in a few weeks assuming that happens due to coronavirus) and we're still planning to progress as normal. we're in a strong position in that we're living in a bungalow onsite while the build will progress so if things take a bit longer to arrive due to the supply chain then so be it but I don't see it as a reason not to start at least. As John says, we can get the foundations done and order the TF and windows once a confirmed date for the TF is obtained etc. but everyone's situation is different and what works for us might not work for others!

indeed it has. https://national.homebuildingshow.co.uk The National Homebuilding & Renovating Show has been postponed The Homebuilding & Renovating Show has been following Government guidelines regarding the continuation of our event surrounding the outbreak of Coronavirus. However, as the news has been progressing we have listened to the concerns, from all parties, around the health and welfare of their staff. As a company we are becoming increasingly concerned for the wellbeing of our visitors, exhibitors and staff, and as this is our first priority, we have taken the extremely difficult decision to postpone The National Homebuilding & Renovating Show at the NEC, until the Summer. We are now working through the ramifications of this unprecedented situation. Please bear with us while we try to establish new dates. We will be in touch with all our visitors as soon as we have more information to share.