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.
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?
This newsgroup posting comes to you directly from...
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
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.
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.
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.
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)
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.
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)
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.
It depends on the IR band
Remote controls are in the near IR band up to 1.1 um and can been seen
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
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))
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.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.