Insulating a garage

[Snacker]

I realise that garage insulation questions are pretty common on here, but I'm more interested in asking whether or not it's worth me doing rather than how to do it.

I've got a brick-built detached (1978) house with an attached garage of the same construction (also pitched roof) but single-skin walls all around including the wall adjoining the house. It's got a concrete floor and a steel up-and-over door.
The interior walls are all bare brick but the ceiling has been boarded and skimmed. I'm presuming that the 'loft' space above hasn't been insulated but I'd need to cut an access hole in order to check for sure.

My question is, am I likely to notice much difference, in terms of heat lost from the house and heat lost from the garage itself, just by fixing 50mm Celotex to the inside of the garage door and then fixing Celotex insulated plasterboard to the wall adjoining the house?

I'm concerned that as it stands, the garage is acting like a massive heatsink and leeching warmth from the house and then to the outside air via the garage door.

 

[dishman]

I suspect that your "attached" garage is (although connected to the main house) attached to against the outside cavity wall of you main house.

If this is so. Then far from "leeching" heat, it is already probably providing some insulation and weather protection to the exterior wall it is attached to.

I doubt insulating your garage to prevent heat loss from your house will do much at all, as you already have a cavity wall (and possibly another single skin wall in the way.) Unless you heat the garage, insulating it will do nothing.

Unless you are converting the garage, I would think it would be a waste of time if your aim is to prevent heat loss from the main house.

I would look more at house insulation (loft, wall) and draft proofing, doors etc will be of far greater benefit.

 

[Snacker]

I suspect that your "attached" garage is (although connected to the main house) attached to against the outside cavity wall of you main house.

Is there an easy way to figure this out, short of drilling through the wall? The reason I think it's a solid wall is because, from the outside at least, it looks like it's only one course of bricks thick, although it's not that easy to tell due to the way that the front porch has been built.

Unless you heat the garage, insulating it will do nothing.

It's heated fairly regularly as I use it as both a gym and a workshop, and there's both a radiator and a fan heater in there. Would the Celotex on the door make much difference in keeping the heat in? I've already filled pretty much every gap I can see using expanding foam, silicone and adhesive foam strips where applicable so there aren't any draughts at all anymore.

I would look more at house insulation (loft, wall) and draft proofing, doors etc will be of far greater benefit.

I've already done all of that so this is the last area to focus on really (although I haven't opted for cavity wall insulation as I'm still really dubious about it given some of the negative feedback I've heard/read).

 

[dishman]

If it is a 1970s house, unless non-standard construction, it must be cavity wall. Measure from the outside wall of a window to the inside wall. It should be around 300mm thick. A solid wall will only be a brick length thick.

The only thing insulating the garage will do, is keep the garage a bit warmer for longer. I doubt it will have much effect on heat loss from the house.

As I said, the garage is already insulating/protecting the side of the house.

The sides of the house without the garage will lose far more heat than the side with the garage. What is more comfortable, to stand in the garage, or to stand outside it....

You may want to re-consider cavity wall insulation if you want to insulate the house more and keep it warm. As long as it is done by a reputable company. It is just one of those choices....my 1930s house had its cavity walls insulated with rockwool in the 1970s! There were a spate of damp problems around that time that cause a lot of concerns, however my house hs not suffered from any. The cavity wall ties may have begun to rust and need replacing, but they probably would need doing by this time anyway..

By all means insulate the garage door. As I said, this will just keep heat in the garage a bit longer. It will have little effect on the house.

 

[Snacker]

If it is a 1970s house, unless non-standard construction, it must be cavity wall. Measure from the outside wall of a window to the inside wall. It should be around 300mm thick. A solid wall will only be a brick length thick.

My problem is that there's only one window in the wall that adjoins the garage, and that doesn't open, so I've no way of measuring it. However the rest of the walls definitely have a cavity so presumably that one will too.

Thanks for your help. In that case I'll just insulate the door and maybe stick some insulation in the garage loft so that it holds the heat better when it's in use.

I'm still torn on the cavity wall insulation thing for the very reason that you mention. The last thing I want is to start having problems with damp.

 

[dishman]

Damp occurring after cavity wall insulation can be caused by more then one thing. Here are two.....

One reason may be that the material filling the cavity allows moisture to bridge from one side to the other. With modern materials this should not be likely to occur.

Some have the opinion that old type cavity wall ties (which can be prone to rust, as they were not coated etc.) may degrade quicker. I do not know the type of wall ties used in the 70s. They were probably a better material than used in the 30s. As I said, my wall ties are probably rusting now anyway (regardless of my cavity wall insulation), and could probably do with replacing.....


The second cause is more down to the home owner and house use habits:

We create a lot of moisture in our houses on a daily basis. As we insulate and draft proof, we often cut too much ventilation out. Moist air is trapped in the property for longer. Moist air will then form as condensation on cold surfaces. If we install cavity wall insulation, the walls will be a bit warmer. In old houses there will always be small areas we cannot access to insulate. So you may get a cold spot on a warm wall. The moisture will now get concentrated onto a smaller cold spot. Hence you get more concentrated damp. People then notice this "new" concentrated damp and assume that the cavity wall insulation has directly causes it, when in reality, it has not. As I said this can easily be solved by installing adequate mechanical ventilation in kitchens, bathrooms and changing living habits.

Again these are only a possibility, and depend on the design of your house and how well ventillated it is. So you many not get either of these issues..

There will be a variety of other causes and opinions...some surveyors say a cavity should stay a cavity. Others I know say you should insulate and the chances of their being issue is small.