Adhering to thermal requirements when re-rendering

housebuyer7

Hello,
The rear of my terraced property is rendered and it was in very poor condition and causing damp. I’ve had it all hacked off and just letting the brick dry out while I decide to do what next!

Property was built about 1900 / 1910 and is brick. I am not staying for long and just want to sell in the next year or so. As such I don’t want to spend too much on this.

i am aware of the thermal requirement since the re-rendering is going to cover over 25% of my property. I haven’t a clue how home owners are expected to calculate U values and all the builders I have spoken to also don’t know how to do it! 

So I am wondering does anyone have any recommendation for some insulation? Requirement would be the absolute minimum amount possible in thickness, least expense, and least amount of work required attaching to the walls! Will adding this be sufficient for building control? Can they sort out the calculations themselves from there? Or will I still need to provide post insulation calculations? 😔

FreeBear

housebuyer7 said: i am aware of the thermal requirement since the re-rendering is going to cover over 25% of my property. I haven’t a clue how home owners are expected to calculate U values and all the builders I have spoken to also don’t know how to do it!

The calculator I use is this one -> https://www.changeplan.co.uk/u_value_calculator.php

For a solid brick wall, your base line u-value will be around 2.0 W/m²K with a target of 0.30 W/m²K - For a Victorian building that is already suffering from damp issues, you should really be using breathable insulation & render. Woodwool boards or cork topped off with a lime render would be best. Using EPS or PUR/PIR with a K-Rend finish would be the approach most builders would go for as it is cheaper. Still going to cost a fair chunk of money though.

However, there is a little cop-out clause in the Building Regulations - If the simple payback period of insulating against energy savings exceeds 15 years, then you should do the best possible within the constraints. If you can make other thermal improvements (e.g. low e double glazing or increased loft insulation), these can offset the requirement for EWI.

To be perfectly honest, you are never going to see a dramatic cut in your heating costs with EWI on just one wall, and certainly not enough to justify spending £££ doing so. If you use something like ecoCork, you'll get some insulating effect, and a finsh of your choosing. Finding someone with the experience of using lime without adding cement to the mix is not easy though. The alternative is CorkSol, but I can find zero information on the binders used, so have great difficulty in recommending it. They say it is breathable and suitable for solid brick walls, but no data to support the claims beyond a single line in the linked pdf.

housebuyer7

Thank you so much! I would have loved to use lime as we have lime mortar but my budget is just a few thousand and that’s already with a loan. I have replaced all the windows so maybe that will help? Financially the best I can do is cement render but I’m struggling what to do about the insulation. 

housebuyer7

Apologies but I do not understand that website. It doesn’t seem to let me input how thick my internal walls are?

housebuyer7

How do I calculate the savings vs costs for the cop-out? I was quoted £13,000 for lime.

FreeBear

housebuyer7 said:

How do I calculate the savings vs costs for the cop-out? I was quoted £13,000 for lime.

Does that £13K include any insulation ?

£13,000 over 15 years is £866 per annum - If you can not make that kind of saving on just heating each year (based on current prices), then it is not economically justifiable. According to USwitch, the average gas bill is around £853 (I would expect a terrace house to be less) - No way you would make a 100% saving (more likely 5-10%), so you'd meet the requirements for the BR cop-out.

housebuyer7

Thank you so much! How do I advise this to the BC? Does this mean I won’t have to supply u value calculations? I am doing other thing to improve the thermal element such as new windows throughout.

FreeBear

Take your current gas bill, multiply it by 15. Show BC that the £13000 is more than you would spend on gas so it fails the simple return on investment calculation. That said, they may well take a look at the costing and not insist on the insulation without any further input from yourself.