ICE HOUSES AND 



Sawdust is the most common insulating material, be- 

 cause it is cheap, and, in many localities, easily obtained. 

 Sawdust from woodworking factories is usually dry, but 

 from other sources it is likely to come from green lumber and 

 be wet. Wet sawdust moulds quickly, as it has the elements 

 of decay in it before it is ever placed in the building. Damp- 

 ness not only causes the sawdust to rot and settle, leaving 

 uninsulated spaces in the wall, but also reduces the value of 

 the insulating material about one-half. Beams and joists 

 around which it is packed decay, producing an objectionable 

 odor, resulting in the final ruin of the structure. Sawdust 

 should never be used, except in very cheap buildings, unless 

 thoroughly dry and so protected that it will always re- 

 main so. 



Other materials of about the same class as sawdust are 

 cotton seed hulls, chaff, leaves and cut straw. Mill shavings 

 are more expensive than sawdust, but are quite commonly 

 used. They are usually dry, since they come from the out- 

 side of the lumber, which is its dryest portion. Shavings are 

 baled and stored under cover. In such form they are con- 

 venient to handle, and usually sell for from 15 cents to 25 

 cents per 100 Ibs. Shavings are elastic, do not settle readily, 

 do not absorb moisture as easily as sawdust and are free from 

 dirt, bark and chips. Shavings from softwoods which are 

 odorless and not as brittle as those of hardwoods, are prefer- 

 able. Shavings which are damp but which have not started 

 to mould may be dried out and used. 



Mineral wool, known also as granite rock wool, slag 

 wool, rock cotton or rock cork, is a good insulator in spite 

 of the fact that it is made from a material which has a 

 relatively high conductivity. Slag wool contains about 92 

 per cent air space, while the best rock wool when loosely 

 packed contains 96 per cent. While mineral wool will not 

 rot, it needs perfect protection from dampness, for it absorbs 

 moisture readily. If the moisture freezes in the wool the 

 expansion breaks the brittle fibres and thus its insulating 

 value is destroyed. When the wool thaws out it will settle, 

 leaving large unprotected spaces in the wall. Mineral wool 

 costs from $25 to $30 per ton and, as ordinarily placed, will 

 cost four cents per square foot per inch of thickness. Min- 

 eral wool should be free from all solid pieces and when 



Ten 



