Insulating walls with Spray foam and fiber. Need Help ...

[christper2000]

Hi,
I purchased a house recently and I just tour out all the exterior walls in my living room. There was only 1 inch of Cotton insulation, Yes cotton , I don't know if they still use cotton for insulation but it doesn't seem to work very well. Anyway I have 2 x 4s in the wall and I want to spray just one inch of spray foam since it costs alot. After the one inch of foam, I want to add R 13 fiberglass. I know I need 3 1/2 inchs for the R13 fiberglass so I am also adding a 1 x 2 on all the 2 x 4s so it will become 2 x 5s then add drywall over that. Know I dunno if with will work. I need advice on this. I want to use the 1 inch spray foam though so the walls are air tight.

thanks,
p.s. I live in New york so the climate is cold and hot.

 

[Deluks]

Howdy pard'ner! This is a UK based website so any advice given will be based on UK building techniques. I'll have a go though.

It doesn't sound like a lot of wall insulation from a UK perspective but I can't comment on your local building codes. If the roofspace has poor insulation (less than 8") then do this before working on the walls, as that's where most of your heat will be lost.

Your plan should work, but be aware that foam insulation, particularly in rigid board form, has about twice the insulation value of fibre type insulation, you will be more effective at keeping the heat in, and the utility bills down.

Have you looked at the cost of buying rigid pu foam board instead? You could cut these to fit between the studwork, gappy and badly cut edges could be filled with foam from an aerosol can.

Use the 2x1 horizontally once the studwork has been fully filled, and fit insulation in between this. If you can use 2x2's the even better.


For airtightness cover the entire wall with polythene vapour barrier before adding the drywall, tape ALL seams and holes and fix the perimeter using double sided tape or acoustic sealant.

I've no idea how much spray foam costs to get installed over there, but were you to use rigid foam boards and install yourself, then you wouldn't have to pay some guys to come out with the spraying equipment, or incur the cost of hiring one yourself.

Sprayfoam is a poorly received product over here. It mainly gets used underneath tiled or slated roofs, and a common train of thought is that is does more harm than good.

In stud walls though, can't see any issues other than expense.

 

[PerryOne]

As Deluks says sprayed foam is very expensive but it does do the best job. However, polystyrene sheets are almost as good and a lot cheaper.
Completly filling the space between the frame will give you a good result.
Having said that, the wood frame will then be the weak point, this should be covered in turn with two inch thick sheets of tightly butted polystyrene and finished with drywall.
If you do not have the two inches of polystyrne between the drywall and the wood frame, you will find that in time, the water vapour from the air in your home will settle on the drywall and you will have what we call ghosting -where the shape of the wood shows though the drywood as a wide grey line.
Note: polystyrene is three times as good an insulation as fibre glass and it does not sag, it is almost waterproof and the wind will not blow through it.

 

[mointainwalker]

PerryOne

Can't agree with your comments on the insulation value of polystyrene.

I believe the following is correct.

Fibreglass and expanded polystyrene - same insulation value ( 100 mm both R 2.5)

Extruded polystyrene - 40 % better ( 100 mm R 3.5 )

Polyurethane - 50 % better. (100 mm R 4 )

Note to the OP:

US and Europe use different formulae for R values, so don't worry if these numbers look strange t you.

 

[noseall]

PerryOne

Can't agree with your comments on the insulation value of polystyrene.

I believe the following is correct.

Fibreglass and expanded polystyrene - same insulation value ( 100 mm both R 2.5)

Extruded polystyrene - 40 % better ( 100 mm R 3.5 )

Polyurethane - 50 % better. (100 mm R 4 )

Note to the OP:

US and Europe use different formulae for R values, so don't worry if these numbers look strange t you.

Perryone does not know the difference between polystyrene and foam board insulation unfortunately and continues to mislead posters.

 

[JohnD]

the difference between polystyrene and foam board insulation

Polystyrene is much cheaper, and is white? Foam insulation board has shiny foil layer?

 

[hotrod]

PerryOne

Can't agree with your comments on the insulation value of polystyrene.

I believe the following is correct.

Fibreglass and expanded polystyrene - same insulation value ( 100 mm both R 2.5)

Extruded polystyrene - 40 % better ( 100 mm R 3.5 )

Polyurethane - 50 % better. (100 mm R 4 )

Note to the OP:

US and Europe use different formulae for R values, so don't worry if these numbers look strange t you.

I know U is just an inverse of R, but I just can't get used to manufacturers quoting R values. The figures just look odd and make me feel uncomfortable - It's not right!!! We should all work in U values by law! Does anyone else feel like this?

 

[noseall]

the difference between polystyrene and foam board insulation

Polystyrene is much cheaper, and is white? Foam insulation board has shiny foil layer?

...and pir/pur foam board offers a greater degree of protection than polystyrene or fibreglass/mineral wool.

 

[hotrod]

the difference between polystyrene and foam board insulation

Polystyrene is much cheaper, and is white? Foam insulation board has shiny foil layer?

Think Nose is referring to PUR boards (e.g. Celotex and Kingspan) as opposed to Jablite.

 

[mointainwalker]

@ hotrod

Really don't understand why you seem to "hate" R values.

Both R and U are necessary and I think, psychologically, most people are happier with whole numbers and the "logic" of an increasing number being better.

 

[hotrod]

Really don't understand why you seem to "hate" R values.

Hi mointainwalker, I don't "hate" R-values per se, it just seems that after years of dealing with U-values people and manufacturers are now starting to "talk" in R-values. Why is this? I notice your location, maybe it's to do with harmonisation of European standards and regulations, because it's only in the past few years I've noticed R-values becoming more widely used over here. When I first started dealing with heat loss at university everything was dealt with and calculated in terms of material thermal conductivity and hence U-values were used. R-values were never used.

Both R and U are necessary

But they aren't both necessary. If you know the U-value of a material and its thickness you can calculate the R-value.

and I think, psychologically, most people are happier with whole numbers and the "logic" of an increasing number being better.

If you think about it logically though, the lower the U-value the better as it's a measure of thermal conductivity and when you've been dealing with them day in, day out for years it becomes second nature. Conversely, for an R-value, yes, the higher the better as you are dealing with thermal resistivity, so I can kind of see the benefit for DIY joe down B&Q on a Sunday. However, there must be tens of thousands of construction professionals who have been brought up on U-values and U-values are still the SI unit used in the Building Regulations in this country. [/rantover]

 

[mointainwalker]

Hotrod

Really don't understand your point.

If the R value is there the people who want a U value will calculate in about 0.25 secs whereas the DIY Joe you speak of will be left floundering by a U value.

Therefore using your number of tens of thousands of construction professionals interested in U vs several millions who can more easily understand R, the latter is, in my opinion, of far more general use.

Anyway, no more from me on R or U