Insulating garage roof regs

[Alec200]

I'm looking to cheaply insulate my detached double garage. It's a single brick wall construction with a tiled pitched roof with a membrane underneath. I use the space in the pitch for storage so don't really want to loose that.
I'm just doing the basics at the moment. Insulating the single skin up and over doors and sealing any gaps around them. I've just started using a desiccant(sp?) dehumidifier to reduce RH in low winter temps. It's quoted to work down to 1 degree Celsius. The unit exhausts air 10 degrees above ambient so has some heating value too. I'd like to further insulate the garage and thought the roof might be a good place to go next. Due to the arrival of my baby girl last week, the work must be cheap and not labour intensive.
I know little about construction and regs so though I should ask before I start planning! I guess something like rigid foam sheets would be cheap, but do regs/basic safety require that I board over them with something to act as a fire retardant? I use the garage to store an old car I've restored, and I don't really want fibreglass fibres etc floating all over the place. I've sealed the garage floor with specialist paint and white washed the walls with exterior masonry paint.
Thanks for any help
Forgot to say that I presume that I can't just stuff silver foil wrapped fibreglass insulation between the rafters as an air gap is require under the membrane?

 

[tony1851]

There are no regs for insulating a garage because it's exempt.
Really its up to you what you put in the roof, though there is no need to go overboard as it will always feel cold.

 

[Alec200]

Thanks for the reply. After starting the topic I duplicated it in the Building section of the forum as I guess it relates to that more.

 

[dhutch]

I guess the first question is, why are you trying to insulate it? How good do you want it to be, and for what reason?

 

[^woody^]

Unless you have an insulated floor, insulated cavity walls, insulated garage door, totally draught proofed openings and above all, a heating system to produce the heat you want the roof insulation to keep in, then it's a bit of a waste of time

 

[Alec200]

I use the garage to store and work on a car I've spent about 1400 hours, and many thousands of pounds, restoring. My chief aim is to create an environment that will limit, as far as reasonably possible, rust. Humidity seems to be the major concern. Heating the garage as it stands, would be very expensive. The route I've taken so far is to run a desiccant dehumidifier and plug big gaps around the garage door. I've just started monitoring the Relative Humidity/temp in the garage to compare to those outside. I don't know what would be a good level to get the RH down to, but lower is better. Elevating the temperature in the garage obviously reduces RH.
I guess that making the garage less draughty will reduce air exchange with the outside airs higher RH. My idea is to insulate the garage better so the air exhausted from the dehumidifier will elevate the garage temperature enough to keep the dehumidifier working efficiently-certainly over one degree Celsius and the higher the better.

 

[noseall]

Surely a de-humidifier is a waste of time in a space that neither heated or sealed from outside. The garage door will be leaking in air like a barn.

You seem to be struggling to achieve something that is not achievable with your current set up. In other words you would need a sealed insulated box to be able to see the effects of your efforts, with controlled heating and air exchange.

 

[freddiemercurystwin]

With a new baby, unless you're from the dark ages, you may as well lock the door up and seal it up for the next couple of years!

 

[Alec200]

You're probably right. But during that time I want to limit, as far as reasonably practical, the car rusting.

 

[dhutch]

If you prime concern is rusting, I would be for INCREASING ventilation to get rid of the damp that will be coming in through the walls etc.
- Your keeping the rain/sun/frost off it, which is the main thing, you just need to keep the air changing so you dont get condensation.

And get a can of ACF-50 to spray on any bare metal parts.


Whats the car?



Daniel

 

[Alec200]

Well I've installed two remote weather sensors. One in the garage one outside. They both link to a wireless receiver in the house. I'm running the dehumidifier at its lowest setting which consumes 340W. At 4 in the morning, after baby feeding, I had a look at the receiver. Outside was 99% humidity and 4.6 celcius. Inside the garage was 63% RH and 8.8 celcius. Just now, at noon, the readings are 75% RH/8.7 celcius out and 62% RH/8.6 celcius.
To me those results are promising. A significant drop in RH. All I've done in the garage so far is Thermawrap one of the garage doors and seal up half the gaps around that door.
I can see the theory of maintaince good air exchange with the outside to remove moisture. But with a desiccant dehumidifier running, I think the opposite would be true. I'd bee interested to see people's thoughts on this.
The car is not special by conventional standards, but I really enjoy it. It's a 1999 registered Nissan 200sx S14a 2L turbo. I've stripped the entire underside of the car down to the floor pan. That's literally everything off; drive train, subframes, brake/fuel/clutch lines, suspension, clutch. All the components have been either replaced or the rust removed and treated with a quality anti rust paint system. Ive rebuilt one of the sills and fabricated several other parts from scratch. The engines been reconditioned and fitted with forged pistons and running just shy of 300bhp. I could bore you with far more detail of what ive done to the car but i wont!!
The car doesn't go out in the rain or on salty roads. I aim to keep it for many years to come, hence my interest in stopping the rust. I have seen a product called a Carcoombe(sp?), its essentially a bubble that encapsulates a car with RH/temp regulation. That's not really for me though, as I aim to use the car most months of the year and don't want to be deterred from using it by the big effort of removing the car from the bubble, replacing it, re inflating it etc.

 

[mointainwalker]

I agree with dhutch. Making the garage warmer permits the air to hold more moisture.
I suggest no heating, no de-humidifier and big air-gaps under the eaves

P.S. My opinion (and some experience) is that unless you are buying professional equipment , humidity measuring-devices are pretty useless.

 

[Alec200]

Looks like this is a tricky subject then.
I agree that consumer RH meters are rarely accurate to more than 3%. although their readings can be corrected using a simple test using a salt paste to achieve 75% in a sealed container-but less than ideal.
I of course accept that the capacity of air to hold moisture increases with temperature. But I would have thought that the key factor is the relative humidity. The higher this is, then the more moisture will condense on the metal of the car promoting corrosion? I don't see the logic of allowing as much atmospheric air as possible ventilate the garage when the ambient air has say 95%+ RH as it often does during the winter months. At present, according to the average reading of 4 humidity meters, the garage RH stays around 75% when the ambient RH is up to 99%. During the restoration, at the coldest times of year, I would often walk into the garage to find water condensed on the car. So far, when ambient has been 99%+ RH and 0 Celcius, this hasn't happened.
These are just my thoughts so far, I haven't done any serious research into the best way to inhibit corrosion-so all thoughts welcomed

 

[mointainwalker]

But I would have thought that the key factor is the relative humidity. The higher this is, then the more moisture will condense on the metal of the car promoting corrosion? I don't see the logic of allowing as much atmospheric air as possible ventilate the garage when the ambient air has say 95%+ RH as it often does during the winter months.

I think the key factor is temperature differential. If there is no difference between external and internal air temps and humidity, then condensation will simply not happen

 

[mointainwalker]

[quote}But I would have thought that the key factor is the relative humidity. The higher this is, then the more moisture will condense on the metal of the car promoting corrosion? I don't see the logic of allowing as much atmospheric air as possible ventilate the garage when the ambient air has say 95%+ RH as it often does during the winter months.

I think the key factor is temperature differential. If there is no difference between external and internal air temps and humidity, then condensation will simply not happen