You've caught my eye with mention of SIP (it's what I do), so a few things there:...I'm not up with the technical issues associated with air tighteness etc but I have been told that it is possible to achieve high levels of air tightness with a block build - obviously if the builder does his job! I suppose the real issue here is if not going with an airtight timber frame of SIP system is MVHR still worthwhile?
A secondary issue here relates to the Building Regs and the installation of solar panels. I was of the view that if you installed a renewable heat source like a geothermal heat pump this obviated the need to go with solar panels, at least that is what I have been advised. Thanks in advance
1. Even built well, unless you undertake a specific airtightness 'programme' in a block build, it will not be airtight. This is simply a reflection of the properties of blocks/etc. You can of course make it airtight, but that is a distinct separate task, and trade. And it brings a cost with it.
Another limitation is that you're only talking about walls - the roof is another huge issue, as is the connection of it, to the walls. Again, you're talking about time and materials. And , again, money. As you probably know what a SIP is, you'll know this is a non-issue in a SIP system.
2. As to the value of going with MHRV etc, well the fact is, that airtightness is now a measured requirement, so if you have a particularly good reading, you're probably going to need it anyway. Simply put, the choice of your building method shouldn't be influencing your decision on the MHRV, as your requirement for airtightness is the same, irrespective of the build type you choose.
3. In any modern house, built to a high standard, and working well, it's requirement for heating will be (relatively) low. This being the case, heating system choices, and their costs, need to be considered even more carefully than before. I like solar, because, in a new build, it is not a big cost as part of a new system, and imho, it does make a measurable contribution. As usual, YMMV and all that
4. I'm still not personally convinced about heating systems that are heavily reliant on electricity. Again, this is not a reflection on the systems themselves, but more the cost of electricity itself.