Cavity Wall advice

My house was built in 1988. The cavity walls are filled with slabs of rockwool stuff - possibly not as well as I would have liked.
Occassionally I get salesmen trying to sell me the sort of injected cavity wall insulation. They usually claim there is a grant toward it.
I don't like to be pressured - I like to decide if it is a good thing.
Any views?
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On 18/02/2020 19:36, John wrote:

Your cavity walls ARE insulated. Tell the salesman to EFF OFF.
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How would they get the existing stuff out? That might be an interesting answer, involving taking the house apart perhaps. I have no cavity walls, but still get leaflets through the door about it and wonder at the waste of rain forest and printers costs at delivering them to houses they cannot fit it to. maybe they will built me a new house? grin. Brian
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They don’t. If the slab stuff has gaps, they can ( in theory) inject the foam stuff to fill them. I’ve heard of it once, how effective it was/is I don’t know.
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On 19/02/2020 08:21, Brian Reay wrote:

How would they establish if the existing cavity wall insulation has gaps?
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On 19/02/2020 09:36, alan_m wrote:

Full-fill cavity wall insulation needs a modicum of care on the part of the brickies, to avoid creating a cement bridge across the top of a batt before the next rows of blocks + bricks are built and also (more importantly) to avoid dropping mortar onto the top of the installed batt before the next row of batts is pushed down into the cavity.
A 4 inch cavity, with rockwool full fill batts should have the same U vaalue as a 4 inch cavity with 2 inch celotex clamped to the inner leaf, leaving a 2 inch ventilated cavity, but the celotex must be tightly fitted, and clamped to the inner leaf using purpose-made plastic 'wheels' that clip over the wall ties. Ideally, the joints should be taped with aluminium tape too.
I've seen some awful new builds near me, built after 2009 where slabs of inch thick expanded poly were just chucked insde the cavity allowed air flow each side of the insulation , rendering it useless.
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wrote:

By using an IR camera outside the house in winter with the house heating turned up full.
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I suspect they didn’t ;-)
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On 19/02/2020 09:36, alan_m wrote:

They drill a number of holes on the mortar lines and put a camera in.
SteveW
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On 18/02/2020 19:36, John wrote:

At that vintage, chances are they are full fill with solid insulation batts. So there will be no space for additional injected insulation.
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On 19/02/2020 08:43, Jim GM4DHJ ... wrote:

Those batts are treated with something to make them water repellent. STill a valid construction method I believe for properties not in those parts subjected to heavy driving rain.
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On 19/02/2020 17:41, Jim GM4DHJ ... wrote:

Do you go munro-bagging in a string vest and plimsoles, Rab C Nesbitt- style ?.
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On Tuesday, 18 February 2020 19:36:57 UTC, John wrote:

The trouble with cavity wall bats is that their effectiveness is entirely dependent on how carefully they were fitted when the house was constructed.
The only way you can tell if there are gaps is by use of an infrared camera. (You have to wait for cold weather, turn the house heating up, go outside and search for hot spots after a bout 12 hours). Or you can search for cold spots from inside. Some tool hire places have IR cameras. It's very enlightening,
The camera can detect "hot" footprints when you walk across a carpet!!!
At one time you could get IR film for ordinary cameras but we've now gone digital.
You can drill a hole in the wall in an inconspicuous place to see what insulation you have. Or you might be able to see in the loft with a torch and a mirror.
There is/was a grant for insulation at one time. Dunno what the current position is.
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On Tue, 18 Feb 2020 23:40:49 -0800 (PST), harry wrote:

Is there such a thing as an infrared filter for a digital camera? If so, the LCD should show the image same as a dedicated camera does.
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On 19/02/2020 08:35, PeterC wrote:

[snip]

Wrong waveband.
Near infrared is just off the end of the visible spectrum at 750-1000nm. You can get IR pass filters but they mainly make trees look white.
Thermal infrared characteristic of objects at ambient temperatures on Earth is in the 10um band with an order of magnitude longer wavelength. You need special detectors and typically germanium lenses to make images in thermal band IR. You can buy add-ons for mobile phones to do a crude thermal IR camera for not that much (or hire real gear for a price):
(Amazon.com product link shortened)
I think there is an Android one too. Don't expect too much as the sensor is only 80x60 pixels interpolated up.
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On Wednesday, 19 February 2020 08:35:48 UTC, PeterC wrote:

I have some IR pix of my house. Taken from the inside on a cold day so you can see the cold spots.. They are astonishing. I have 600mm insulation my house but there were air leaks. (and cold water pipes)
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On Wednesday, 19 February 2020 08:35:48 UTC, PeterC wrote:

yes, you can remove it to ge a little IR sensitivity.

hardly. IR near to red (ie red hot emitted IR) & room temperature emitted IR are not the same frequency range.
NT
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On 19/02/2020 07:40, harry wrote:

Different IR band to the cameras designed to detect heat loss, and you can still make a digital camera into an IR camera. The IR band used to detect heat loss, say, from a house is blocked by glass so the glass lenses used in a conventional camera would stop their use for this application in either a (modified) digital camera or a film camera.
The sensors in digital cameras/phones can see IR up to around 1.1um although most may have a filter to exclude some or all of the near IR band. Point your phone camera at the output of your TV remote and press any button and maybe you will see the IR LED flashing. Iphones may have a IR filter on the back camera but possibly not on the front camera.
Military IR cameras and those commonly becoming available for industrial or consumer applications operate in the 3um to 5um band or the 8 to 12/14um band. Cameras fitted to the police helicopters are probably the latter. These cameras most probably have Germanium lenses. To keep costs low (to perhaps a couple of hundred quid) consumer IR cameras may be limited to 64x64 or 100x100 true pixel sensors and have small "slow" wide angle lenses and low video frame rates.
A £400 IR camera attachment with a 160 x 120 pixel sensor.
https://www.youtube.com/watch?v=Oiv7sEXL1cI

IR has no colour hence a native B&W video output. This video output is usually modified to give a false colour output. Everything light grey to white is rendered white, yellow or red and everything dark grey is rendered black or blue. The grey scale in between is assigned different colours. Many different false colour schemes schemes can be used.
If you have an old digital camera and you want to experiment with near IR (the effect you could obtain with IR film) https://www.instructables.com/id/infrared-digital-camera---the-real-way/
or
https://tinyurl.com/wdu4oey
Try it on a very cheap web cam.
If you have any processed colour film negatives around the bits at the end that are completely black can be used as the filter instead of of the Congo Blue filters mentioned in the above article. You could use two bits(double thickness) of this black negative as a stronger filter.
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It depends on the IR band

Remote controls are in the near IR band up to 1.1 um and can been seen
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On 19/02/2020 09:39, alan_m wrote:

To put that into some context, when I worked on military IR surveillance kit in the late 80's some of the thermal sensors designed for avionics use had a thermal telescope on the end of them - all "optics" machined from germanium, and if memory serves a mildly radioactive coating applied to the interior surfaces. They started at £150K for the smaller ones!

These systems were higher than SD video resolution in the thermal band - basically using highly polished video line synched rotating polygons to project and scan the image onto a fixed SPRITE detector.
https://en.wikipedia.org/wiki/SPRITE_infrared_detector

False colour seems quite popular in the consumer space, but never really seemed to be of interest for military or avionics. (you have a choice of black hot or white hot, and could adjust the gain and offset (the functional equivalent of contrast and brightness))
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Not just cost, export controls start getting tricky when exporting higher resolution/framerate models that could be used for military purposes.

We have a Flir One gen2 at work - it works reasonably well. Worth noting that the older gen2 Flir One has a higher thermal resolution (160x120) than the current gen3 Flir One (80x60) - basically they renamed the $200 One to the $400 Pro (160x120) and then released a worse $200 new model. Buy an old one if you can.

What's nice about the Flir One is there's also a spot temperature measurement you can bring up, to give you a numeric reading. I don't know the accuracy (don't have means to measure surface temperature to calibrate it) but it seems reasonably good.
Theo
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