Had 3 inch insulation in walls birds looked great loved it, venilation was great, lined it with sterling board 7mm, ( maybe ovy1255 needs more dwangs in walls ) Wat diference you will notice, BUT BEWARE, Do Not Attempt if you have MICE, they love it, i didnt have mice problem b4, once they got in walls with heat, food source they thrived, I,ve ripped walls out 3 times, major headache, still got them, and ware thiers Mice thiers CATS, i,v more or less given up, you cant exspect breed decent y/bs we mice running about spreading dieses, while cats hanging about outside at nights, hope this helps you mate, as said great idea and i think birds benifit from it,Atb