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Greetings I am in the early stages of building a single storey oak framed outbuilding around 90m2. I intend to do everything myself to keep the cost down and as I have always wanted to build a cruck frame, indulge and try and enjoy the process. The ground has some clay content and is close to trees so I was thinking about going down the route of an insulated slab which doubles up as the envelope to form the raft. You may be familiar with passive house foundation stuff. The problem that I am finding is that despite being ‘just a large shed’, building control will need to be satisfied that structural calculations are done. To this end I have had some some quotes done and most are eye watering, or reasonable with the proviso I then spend a small fortune on a bespoke polystyrene system. Is anyone aware of any generic calcs for rafts (after all there are tables for timber beams!). Any help of any kind would be very welcome Cain assembly.pdf

Hi I think I understand how U-Values are calculated e.g. (Layer thickness) X Lambda = R in m2 K/W Add up all the R-values for each of the layers and 1/(Total R-Value) = U-Value in W/m2 K However if you look at the calculations from my "As-designed" SAP 2009 report below, the calculated Total R-Value = 5.844 m2 K/W and if you take the inverse of that the U-Value is 1/5.844 = 0.171 W/m2 K and not the 0.14 shown on the report below. Can anyone please explain how the 0.14 was achieved...what am I missing??? Thanks

This post is a deliberate attempt to expose my thinking on MVHR in the hope that someone will see a flaw in what is planned or be able to make a suggestion which -as has happened before- saves us from unnecessary errors and maybe even saves us a bit of money. What have I learned about MVHR before I got here? Avoid standing hot water pipe heat loss. Get the house air tight. Forget cat flaps. Visit lots of houses with MVHR (thanks @VIPMan among several others). Don't allow your postie anywhere near the front door. Forget normal keys. Open the windows if you like, and switch the system off if you like. Many people have MVHR and don't use it or worse, haven't been told how to use it. In the passiv or nearly passivhaus sector use PHPP (again thanks @VIPMan) to estimate your heat requirement (19 Watts per square meter per annum) - in our case 5 Watts short of a picnic. Watch for overheating (10% risk in our case) Getting from numbers on a spreadsheet to buying a system As I've said elsewhere, here be dragons. Let's be kind and say that MVHR isn't well understood. By sellers sometimes but by Jo Public in particular. I've been digging round for two or three years now, and frankly, my heart's still in my mouth. But I have moved on from looking at a house and thinking - oh yeah, lets put a bigger log burner in there... it'll be lovely. Poor life decisions in relation to pensions taught me that. Useful, relative penury sometimes. Makes me think more, and more deeply. So, I start with a PHPP print out, our plans and send it to a company that says 'We'll do a heat-loss calculation for you' Thanks very much Here is one claculation. Hmmm, much to explain there (for me anyway) Take the Total Column: that's the total in Watts of heat that is used: Living Room uses 518 Watts If you add a 50% factor for 'safety' you get 776Watts And (next column) it takes 642 Watts to heat it, ERGO, the MVHR recovers (776-518) Watts With a Heat pump inline (MVHR and HP) I'd recover (661-518) Watts With a heat pump and a Duct heater, I'd recover (679-518 ) watts Not sure what the percentages refer to..... (help @SteamyTea Bottom line, I'll need just over 3 kW of additional heat ; 3077, 3169, 3261 to heat the house to 21/ 22 ish (bottom line in grey) So, what does this tell you? There's two of us, a cat and two dogs: cat =10 Watts, dogs 100 Watts between them, @MrsRA 1kW (hot stuff ) me a bit less, so 2 and a bit kW. Put the hoover on, the oven and a few lights (no hot water see above) and we get close to just right- or needing to open the windows? Answers on a postcard please...............

Budgets and spreadsheets go together like [...........insert your own idiom here..............] And so do errors: errors of fact and errors in formulae. Realising that, recently, every time it rains, I'm in the office trying hard to avoid checking our spreadsheet. Errors of fact Not a great lot to be done here. My only suggestion is to get a mate to check with you. @MrsRA is better at this process than I am, but we still manage to avoid the issue because it's so hard (for that read time-consuming) to do something which 'should' be easy. It isn't. Errors in Formulae Is there anything that can help the hard, detailed, mind-numbing, eye-watering, annoying slog Yes Here is a simple search for all versions of the term 'formula auditing' (because there are so many versions of spreadsheets out there) And here is one website's summary of several approaches to checking formulae in the most common (I think) spreadsheet of all. Just sayin'. Guess what I'm doing this morning.