Search the Community

We learnt how to keep our house cool this summer and thought we'd share what we've learnt in case its of use to others. We're in a timber frame building built to the Passivhaus standard but not certified. We don't have an ASHP, so no slab cooling for us but without a doubt our (not so secret) weapon are the external blinds. All our east and south facing windows (with the exception of 3 east facing windows - more on them later) have external blinds and as predicted by the PHPP these are the game changer. Our secret weapon is the little personal weather station (PWS) in the garden and with it's help this is how we've kept the house cool: In the evening when the outside temperature according to the PWS is below our target internal temperature of 21 degrees all doors and windows are opened and the MVHR ramped up. Overnight all the inward tilting windows are left open with the MVHR staying at a higher level and it stays like this until the PWS shows that the external temperature is rising towards our target 21 degrees - that happened at 07:50 this morning. As soon as the exterior temperature reaches our target then all doors and windows are closed and the MVHR is reduced to its lowest setting, we monitor the air quality with a couple of CO2 monitors as recommended by @Adrian Walker and increase the MVHR speed as required to keep good air quality. All sun facing windows have the blinds down, we have the mesh style blinds that don't block off the light but stop lots of UV. With this technique our hallway temperature has peaked in the early evening at around 21-22 degrees and the kitchen/dining room which has lots of east and south facing glazing has stayed below 24 degrees. As soon as we open up we get rid of most of that unwanted heat. The hallway starts in the mornings around 19-20 degrees. The reason I think the PWS is a secret weapon is as far as I'm concerned you need to accurately know the exterior temperature and when to let it in and when to keep it out. On a windy day, 26 degrees can feel cooler than 21 degrees but if you let that stuff in the house you're gonna regret it. If you don't have a PWS you'll probably be able to find one situated close to you on the Weather Underground website. Oh, and the 3 problem east facing windows without external blinds: 1 is the utility room. That has an internal blind and as it's the utility room the internal door to the rest of the house is kept closed. That room gets warm 25-27 degrees but the heat stays in that room which of course has an MVHR extract so the heat is slowly being pumped out of the house until it's door/window opening time then we throw the heat away with vigour. 2 is the ensuite which we deal with in exactly the same way as the utility. 3 is the main bedroom which has a great big window and curtains. The curtains remain closed while the sun is coming in that window but the doors are open so as that room warms up its heat is not being contained in that room. As the sun moves round and that window is no longer in direct sun the curtains are opened and a big old chunk of hot air falls out to be slowly extracted until window opening time. To me, its like the house taking a long overnight gulp of cold air and then holds its breath throughout the day until the temperature is 'just right' again.

Hi, I am in the middle of building a timber-frame house (awaiting first fix electrics and plumbing). The recent hot spell has convinced me to get brise-soliel on the south facing upstairs windows. I have them planned for downstairs already. But I played around with PHPP and although my overheating reduced it didn't disappear. My phpp consultant has no figures inputted for L31 window ventilation air change rate and P59 Window night ventilation (in summer vent sheet) Has anyone got 'typical' figures for these? I have used 0.35 and 0.15 respectively and my overheating drops down to 3.9% (with all southern windows shaded). Apart from fitted brise-soliel there isn't much else I can do as all doors windows are fitted and insulation is in place - so I just want to check if the ventilation figures are reasonable. Thanks

Apologies if this is the wrong forum. Am looking at a timber frame (probably) build in the future. Although one requirement will be retaining heat, another one, possibly as important, will be not overheating in the summer. From what I've read then decrement delay can help with this so maybe looking at something like wood fibre insulation or similar. Has anyone experience of this, or designing for it. Alternatively, would you recommend other methods, e.g. MVHR with summer bypass, MVHR with cooling, UFH with cooling, AirCon, solar shades, anything else. Thanks.

Has anyone installed external blinds. I have huge solar gain issues and need shading pdq. I was considering awnings but have seen external roller blinds on the internet and they look very good. Be interested in any feedback and recommended suppliers

Well, finally after years of iterations of drawings in the pre-planning and planning phases we're off to the races! Before I post the final plans I was talking to the Architect today about the potential for overheating shown by the PHPP calculations. I'm going for a Passive House and my concern was rising global temperatures (during the build and more likely afterwards!). The PHPP package allows for 10% of days where the internal temps can rise over 25 degress celcius. That's a lot of days! Not so comfy! The Architect initially aimed for 5%. We delved into it a bit further and I challenged them to improve on this. I did discuss the 3M film which cuts down on long wavelength IR, i.e. drops your Windows G value right down and no more overheating, but, you don't get solar gain in the cooler months either! Bit of a tradeoff. The G values they are using for me currently are 0.6. Other U values are as follows (based on timber framed construction): Floor = 0.12, Roof = 0.1, Walls = 0.125, Doors = 0.96, Windows = 0.84 (These are just placeholders but fairly typical and not hard to meet) I get an A2 rating from the DEAP package which is my preliminary BER. To meet Part L I need one, yes "1" solar PV panel, go figure! Add 5 more panels and I go up to an A1 BER rating, the highest. This assumes a standard Heat Pump and MHRV etc. I'll investigate Passive House Plus / Premium at a later time as that encompasses energy consumption & renewable generation. I should fit 8 panels on the roof comfortably, I'm hoping for more in the back garden at some point. Anyway, what was I on about - overheating! 5% was a bit high given that when I asked them to switch the climate data from Dublin to London it shot up to 13%. Scorcher! By 2050 I wouldn't be surprised if that was the result for this house without a physical move! I want to build for more than today and one generation. The 5% figure is based on having internal blinds on both the rooflights and south facing windows, and opening the windows in the evening to cool down the house if I understood correctly. And that's if you're home during the day otherwise if you forget to pull the blinds you'll be roasted coming home. The MHRV can help a bit but just can't deal with the heat load on a really hot day. I needed to find out what were my options and get that % right down.... I'd read here about the successful use of 3M prestige window film. It drops the G value in half which denotes the level of solar gain the window lets in. The only drawback is while you're cooler in the summer you'll pay for that in winter = less solar gain when you really do want it! It still might be useful for one or two windows and certainly if the temperatures soar over the next decade or two worth introducing then. External shutters are very common on the continent but rarely used in Ireland. As it's the front of the house this could be a planning battle but is it one worth having? You would have to go back to the planners later if so..... Brise Soleil if I've spelled it correctly are those overhanging louvres that are angled to block the worst of the summer sun. With these in place and this is the strategy the Architect is aiming at, it reduces overheating periods to 2%. Then if you start opening windows etc it get's it down to 1%. Blackout blinds are available for Velux rooflights but while they can be motorized, they aren't automatic. Even though the roof lights are on the north facing side, the angle of the summer sun will bring in light and associated heat during the peak months. Internal blinds are of course most likely mandatory but unless they are also automated, they might miss the period of time that would prevent an overheating event. So, right now we're looking at Louvres and internal window blinds. I did see some nice external blinds but these would have to take the weather and I'm not sure if outward opening windows would be compatible? Inward opening windows I feel would leak over time as the seal is pushed in with wind/rain over the years. But that's a different discussion! The front of the house faces just off south at 204 degrees. There's a zinc half porch over the front door and glass window beside it. The windows themselves are tall rather than wide so I'm not sure the Louvres will offer as much protection during the shoulder months but that's probably for the best. The PHPP package was used to drive the 2% with the proposed Louvres size so as long as they stay on the house and don't fly off in the wind, they are probably the solution I'll stick with. Unless the planners have their say! Maybe all I need is electrical windows that darken with a switch....!

With temperatures hitting 25C today this has been the first real test of our house in terms of overheating and how to manage excess heat. When I designed our house, I crunched the numbers, taking into account average and peak daily solar gain. Due to the large amount of SW facing glass that we have, I knew we were going to have some overheating, based on maintaining an internal air temperature of 21C. My number crunching indicated that summer overheating resulting from solar gain could be managed by means of the MVHR summer bypass, and opening a window and ventilating with cooler ambient air, and where appropriate, using blinds or drawing curtains. Up until now, ambient air temperature has always been several degrees lower than internal air temperature making it very easy to control how much of that solar gain we wished to retain. In practice we haven't had to do much in the way of control, as internal temps have not exceeded 23C in the main living areas, the bedrooms remaining 1C cooler as they are on the north side of our site. Today's challenge was how would the house perform without any cool ambient air or active cooling (albeit I do have the capability to cool our slab). I'll be honest and say I was quite concerned, but I'm glad to report that internal temperatures remained lower than external, peaking at 24C in the living areas, 1C cooler in the bedrooms. As ambient air temperature fell to 21C late this afternoon, the summer bypass kicked in and began to ventilate cooler ambient air inside (interestingly, when ambient air was higher than internal, the bypass didn't activate) and I opened two windows, one on the ground floor and the velux on the 1st floor mezzanine to create a natural draw through the house to purge some of the warm air out. This worked brilliantly and rapidly reduced the internal air temperature down to 22C, and shows how effective this method of control is. How did everyone else fare today?

Why do electricians never allow enough slack on loft cables so they can be raised above 300mm of insulation. Its not as if 10”-12” of fluff is the cheapest and quickest way to meet a government requirement, oh wait… I’m not too fussed about the lights, low load, yadda, yadda. However the electric sockets for this room are distributed via the loft not under the floor. I’m not sure if it’s a radial or a ring main circuit. One of the cables has actually been fed through a hole in the ceiling joists. This seems like complete *******ery to me, when all the other cables are laid above the joists. As well as the unnecessary damage to the joists it makes it difficult to lay the insulation as there’s a 50mm gap between the cable and the ceiling. I either squeeze the 100mm loft roll under it and lay 200mm above it or just put the full 300mm over it leaving a small air pocket under the cable. As I understand it, the cables should be in contact with a surface like the ceiling or a joist OR they should be open to the air so as not to overheat. Although you would normally consider a bedroom to be a low electrical load room – I must consider the use of more than one high load device: hair dryer, straighteners, curlers, rollers, iron etc. I’ve slapped 100mm of roll over it for the moment as it was bloody cold without it but I wonder what is ALARP before I put the other 200mm over it?