What is used in the windows as a thermal break is blocked by the glass and metal so there is no need to worry about any offgassing. The most extremely sensitive clients can smell the edge of this thermal break and some glues used.
Wood - Wood windows are usually treated with fungicides. You could use a sealer that seals in VOCs like AFM Safecoat Safe Seal, AFM Safecoat Transitional Primer, or B-I-N Shellac Base Primer & Sealer. You could go with custom wood windows to avoid fungicides, but they are more expensive and you still have to consider what kind of sealer you can tolerate on the inside and outside. Finding a suitable sealer for outdoor wood is tricky. AFM Safecoat Durostain or AFM Naturals Clear Penetrating Oil are two options. The outside would need to be re-stained on a regular basis.
All wood windows are not a good idea but you can consider ones that are wood on the inside and a more weather resistant material on the outside. Consider also the glue that is used in conventional wood windows could be irritating for the sensitive person.
Fibreglass - Fibreglass offgasses VOCs and some very sensitive people do report reacting to it. Though may be tolerable for many.
Vinyl - Vinyl is generally not healthy, but since this is a hard plastic many very sensitive individuals report tolerating it.
Gas filled - Windows filled with argon or krypton gas have a higher insulative value and both gasses are considered non-toxic.
Silicone - My top choice for silicone is Eco-Bond but I review a few different options in this post.
Sealing around windows and doors - Wool products can be used instead of polyurethane foam. Or non-toxic plastic backer rod can be used. I don't find that this has a scent.
For zero-VOC window flashing use TYPAR AT. They do not recommend this being used in the rough openings and it doesn't fit all building codes.
|Source: Blinds Chalet|
Fabrics - Fabric curtains are usually treated with wrinkle-free chemicals and flame retardants. Natural fabrics do break down in UV light but are a better option.
Blinds and Shutters - Green versions include naturally finished wood shutters, metallic venetian blinds, and bamboo roll down blinds.
Between the Glass - Between the glass is a really cool option. Here is an example.
Non-Toxic Blackout Shades - This is a hard to come by product. Blinds Chalet blackout liner on the bamboo shades is PVC- free and they claim that it is environmentally friendly. Earthshade makes eco black out shades and rollers that are probably the safest ready-made option on the market. Another option to consider is this paper Black Out Pleated Shade - the company claims in an email they do not give off any hazardous chemicals (I use the natural colour version of this - it has a slight toxic smell and needs to be offgassed for a bit). Another really safe option (truly the safest) would be to make your own black out curtains with pesticide-free hemp fabric.
Avoid vinyl roller shades and vinyl miniblinds, PVC and conventional blackout curtains.