It's a wood fiber board with a thin asphalt coating often called "buffalo board" or "beaverboard", the trade name of the long defunct Beaver Board Co. It was an inexpensive exterior wall sheathing.
Beaverboard®, black board, buffalo board, gray board, cane board, Celotex®, Homasote®, Insulite®, Nu-Wood® are some of the many names of fiberboard or plant-fiber board sheathing products used on roofs, exterior walls, interior walls & ceilings.
Unless the fiberboard actually absorbed water, can't be dried, and / or is damaged, replacing it is not likely to be cost effective nor necessary. Unless there is a serious mold problem I'd leave the sheathing in place.
Underlayment Underlayment or weather resistive barrier (WRB) is installed between the siding and the sheathing. This can be tar paper or a house wrap such as HardieWrap® or Tyvek HomeWrap®. HardieWrap® is great for keeping water out and at the same time letting water vapor escape from the house.
Asbestos in Low Density Board (LDB) "Fiberboard" Products. Some low density fiberboard products like those described here were widely manufactured and distributed including in the U.K. and Australia; these products are particulary hazardous if disturbed as they are soft and they contain high levels of asbestos.Dec 15, 2012
Mod. OSB wafer board does not contain asbestos. And OSB wafer board is not a fiberboard product but rather is made of wood chips and glue.
Fiberboard cement siding can be hand-nailed, but because it's so much harder and more brittle than wood, you have to predrill holes near any edge.Jul 14, 2021
Re: Vinyl siding over Celotex Absolutely not, vinyl siding will not have any strength to offer the structure on its own. If you really can not afford to do it properly then I would remove any rotted old siding and replace it with plywood and then install house wrap and vinyl siding over that.Feb 2, 2013
Fiberboard structural sheathing is an engineered product made with ground up wood chips and lumber waste glued together with an asphalt binder or resin. The finish of fiberboard is uniform, with no knots or grains like those found in real wood.Mar 25, 2020
Question: Do you put plywood under siding? Answer: If it's plywood sheathing, yes you can put it under the siding. It'll be the best structural support for your house.Mar 16, 2021
Even the United States Department of Energy (DOE) agrees that “when new siding is to be installed, it is a good idea to consider adding insulation under new siding.”Mar 1, 2018
Yes, DuPont™ Tyvek® WB can be used under any façade, including brick, stucco, vinyl, cedar siding, metal, and stone. Proper installation under each façade is essential to ensure Tyvek® provides the maximum level of air infiltration resistance and bulk water holdout.