Foam Injection in Aluminum Windows

Old 04-10-07, 08:31 PM
Thread Starter
Join Date: Apr 2007
Posts: 1
Upvotes: 0
Received 0 Upvotes on 0 Posts
Foam Injection in Aluminum Windows

I have a case of Great Stuff expandable foam. I was wondering if I can increase the STC (Sound Transmission Class) and reduce the air draft, if I were to inject the foam into the hollow chambers of the frame of my dual pane aluminum windows. Are there also any other tricks to dampen noise energy hitting the aluminum? I just place a customized order of duel laminated panes of glass to retrofit my windows for the front of the house, as the street is busy with traffic. I'm hoping this will make a significant reduction to the traffic noise as well. Please offer any feedback you have.
Old 04-11-07, 03:49 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 36,608
Upvotes: 0
Received 9 Upvotes on 8 Posts
Not sure how you intend to access the area, but I guess you have that figured out already. Expanding foam is not the right stuff to use on windows or doors. If it expands too much, your windows will become fixed due to the pressure exerted on them from the foam. You should use minimally expanding foam for windows and doors. I know you already have a case of the stuff, just make sure it says it is minimally expanding, or for windows and doors.
Old 04-11-07, 04:28 AM
Join Date: Oct 2006
Location: Wilmington
Posts: 3,994
Upvotes: 0
Received 0 Upvotes on 0 Posts
If those windows have thermal breaks, you don't need the foam, if they do not, foam may destroy them, as suggested above. Most manufacturers realized decades ago that aluminum was not a good energy efficient material for windows. What you suggest will likely not help, but definitely may hurt.
Old 04-12-07, 05:49 AM
Join Date: Oct 2004
Location: United States
Posts: 180
Received 12 Upvotes on 9 Posts

STC stands for Sound Transmission Class.

Technically anything that you do in the field does not affect STC - even if it might affect sound attenuation of whatever it was that you may have modified - because STC is a laboratory rating based on some very specific sound pressure measuring criteria. Using STC to compare the sound-blocking capability of different window styles or brands is not a bad idea because a window with an STC of 35 is usually going to outperform a window with an STC of 31; but, STC is sort of like mileage ratings on a new car…not always as accurate as one might hope.

Stopping unwanted sound thru a window (or any other material) on the other hand, is determined by three things – mass, stiffness, and damping.

Increasing the mass of any object will have an effect on sound transmission. Increasing the mass of a window by making the glass thicker will increase sound attenuation, but not nearly as much as might seem obvious. Glass does not play by the rules when it comes to sound attenuation - it cheats.

Besides increasing the mass of glass (or frame if needed) increasing the stiffness of glass would help to block unwanted sounds - however it is physically impossible to increase glass stiffness - at least in the real world - so that leaves damping the sound as the only remaining variable.

Glass inherently has very little damping ability, but placing a layer of a more viscous material between two of lites of glass substantially increases the material's ability to dampen sound – thus the advantage of laminated glass.

As an example, a single pane of 1/4” (overall depth) laminated glass consisting of two 1/8” lites with the plastic interlayer actually has as much sound blocking ability as a 1/2” lite of ordinary monolithic glass - at half the width and half the weight. Laminated glass is a good thing when you want to block sound - as you already know since you have ordered lami for the window that you wish to upgrade.

The lami will help block sound - alot. But, you have to make sure that the window is tight and that there are no airleaks because air leaks will transmit sound. Adding non-expanding foam as part of the install of a window - around the outer edge - will likely help. Adding expanding foam inside the hollows of your existing windows is probably a very bad idea - as pointed out by Chanler and Bill.

Actually, aluminum is an excellent choice for a sound-performance window. Just not the best choice for energy considerations. Aluminum frames are often recommended over other window frame materials in applications where sound-blocking is the primary consideration.

Again, make sure everything is TIGHT and if need be make sure that any possible routes for air transmission are blocked. These measures, combined with two panes of laminated glass, should show very significant improvement in sound performance over your current set-up.

Good luck.

And, just for fun, and for no other reason, here is the reference for determining STC...(not all of the formulas actually came thru this format - but you get the idea!)

A. ASTM E90 - Airborne Sound Transmission Loss, 1/3 Octave Band Data
B. ASTM E283 - Rate of Air Leakage Through Exterior Windows, Curtain Walls and Doors
C. ASTM E413 - Classification for rating Sound Insulation.
D. ASTM E1425 - Determining the Acoustical Performance of Exterior Windows and Doors

A. All tests for validation of window performance for compliance with these specifications shall be conducted by an independent NAVLAP certified testing laboratory.
B. All windows must meet or exceed the minimum requirements of performance class FC for the design load specified in accordance with ANSI/AAMA 101 the requirements for STC Class when tested per ASTM E90 and evaluated by E413.
C. Air infiltration at a test pressure of 6.24 psf (50 mph) shall not exceed 0.0 cfm per sq. foot as measured in accordance with ASTM E283.
D. The entire window assembly (framing members, glass, and integral components) shall meet or exceed the value listed when measured in
accordance to ASTM E90 and E413. The sound transmission loss shall
meet the following deviations:
1) Three non-continuous 1/3 octave band values may deviate below the specified values as much as three decibels, subject to the provision in 2:
2) The summation of deviation of decibels from the specified values must not exceed six decibels.

Tested values for an STC 52 window shall be:
1/3 Octave Bands: 125 160 200 250 315 400 500 630 800
Transmission Loss: 28 39 42 44 45 50 52 52 53
1/3 Octave Bands: 1000 1250 1600 2000 2500 3150 4000 5000
Transmission Loss: 53 55 57 62 64 68 70 75

Formula for calculating the effect of air leakage on sound transmission loss:
10 log10 [1+ .012(L/S)10STC/10]

Formula for calculating the frequency of glass resonance:
1150 t1 + t2 / t1t2d

Where t = thickness if the glass layers
d = separation of glass layers
all units of measure in mm
= square root

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: