Cavity Walls Or Not?

[simoncnx]

Im about to start a build in chiang mai and had thought to put cavity walls for the exterior. Have considered Qcon blocks but here they retail at 24b each for the 7cm block - dont know if that is expensive or not?

My reasoning was good insulation and also thicker exterior walls allow you to have windowsills which i like. However I am concerned about ants termites getting into the cavity and causing problems. In that case would single 20cm blocks be better? Also, whats the best way to insulate the floors and ceilings?

Any comments please

Thanks

Edited October 10, 2012 by simoncnx

[passingas]

I used AAC block on the exterior with a cavity space and put the red brick flush with the inside of the columns. I not only had great window sill area, but no POS column to have to run the ceiling around. I was also amazed at how it sound proofs as well. Without really trying, we ended up with a passively cooled house in the tropics. Termites will never be an issue with composites, but the ant problem...well...let's just say it is no way to keep those buggers out...trust me. Unless you want to live in amongst a toxic dump like atmosphere with poisons and such. Plant marigolds around your house, I have heard that keeps them at bay. I would not worry about the extra cost using AAC blocks, because if you plan to use AC, you will be so glad you did the double wall. As far as floors and ceilings go...is this a condo like structure, or what? Ceilings can be insulated with rolled insulation...we did our MBR ceiling on the second floor, and it works just great....but our roof is a real light blue color and reflects huge amounts of sun light, so the attic area stays relatively cool. I have four custom gable louver vents at the peaks and used the vented soffit all around the overhang, except the porch, balcony and terrace areas. I would say stay away from hip roof designs...they just turn your attic into an oven. Good luck....pg

[Ackybang]

Hello Simon.

I've been slowly self building up on the Cambodian border - building a 200 square bungalow. I chose to do cavity walls in redbrick, as I thought that the acc blocks were expensive also, aswell as the fact that you have to buy special tools / cement / render / fittings to use with them, and then find a builder who's really used to using them - and not just somebody that says they can. The fact that they are quick, and use less cement, render, etc, didn 't mitigate the overall cost for me. Because of their great thermal properties, would probably think about them for a single wall, and if you go for the really thick ones, they are load bearing also, which means you don't, in theory need to pour posts.I found a cheaper composite, a variation on the aerated theme, which can be used with normal concrete / render, but they must be plastered within three Months of laying, and a sample I took, disintegrated quite quickly, left to the elements. Subsequently, I am very happy with the results, so far - apart from feeling very strong and solid, and not seeing any pillars in my house, which I hate - my house, which is far from finished, on a hot day, has an ambient temperature at least 12 degrees cooler than outside in the shade, and many more than the outside temperature in direct sunlight, and that's without yet rendering and painting, which, in addition to u.v. reflective windows, etc, will help to reflect the heat even more. I went for a dark, two tone c-pac roof and used dry-tech, which will allow your roof to breath, and vent at it's highest extremities. Under the C-light that the roof tiles sit on, I added reflective foil which really makes an immediate difference - I would recommend shopping around, as I managed to find end of stock, agricultural foil from New Zealand, guaranteed for ten Years, and much stronger than all the others that were recommended to me, for a third of the price - and just as, if not more effective - regardless of what the merchants and adverts try to tell you. If your stop the foil at least 50cm short of the outer edges of your roof, and use vented soffits, you probably wouldn't need any other venting. Maybe overkill, but I'm trying to future proof against energy use, so will probably lay the fiberglass insulation above the ceilings aswell, when I put them in - you will use a lot less energy keeping the house cool / warm this way. I'm looking at both scenarios, as temperature where I am runs from one extreme to the other, throughout the course of the Year. I don't mean to tell you stuff you probably already know, but If you are going for cavity wall, make sure you, or your builders put in breather pipes, wherever you pour lintels, otherwise your rendered wall will crack. Most Thais, and subsequently 'most' Thai builders don't lay cavity walls, and will overlook this small, but important point. I'm not quite sure what you mean by insulating the floor. Raising your floor off the ground will help to cool your house, as well as minimalise problems with termites, as they don't like to live above ground - don't forget to make your builders block the wall cavity with smartboard, and not plywood before they pour the lintels, and use anti termite treatments on any wood finishings in the house. Ants won't do your building any harm - they only forage and clean up food / dead insects etc, so if your house is clean, you shouldn't have a problem. The village where I live is full of shanty shacks, and bare block houses with tin roofs that have stood for Years - and many are still quite cool and comfortable in the hot Months, because the owners have planted trees around them, to offer good shade, and considered where the sun hits them, at certain times of the day. Plan the layout, and position of your house well, for optimum cooling, before you start, and you won't go wrong. Good luck with your adventure.

[cooked]

Instead of building a double wall onto our as yet uninsulated house, I am now thinking of putting the second wall 200cm from the first, giving us storage space and alternative access to the guest room we will be building. Overhanging roof. And PS: very easy to do it yourself, I built two houses with Q-blocks. You'll make a better job of it.