EXHIBIT 99(a)(4)

Dillon, Read & Co. Inc.



                                         535 Madison Avenue
                                      New York, New York  10022
                                             212-906-7000


                                    April 5, 1996


Board of Directors
Bird Corporation
1077 Pleasant Street
Norwood, MA  02062

Dear Sirs:

          You have requested our opinion as to the fairness, from
a financial point of view, of the per share consideration to be
received by the holders (the "Shareholders") of common stock,
each with par value $1.00 per share ("Common Stock") of Bird
Corporation ("Bird") in connection with the proposed tender offer
for the Common Stock and subsequent acquisition of Bird (the
"Transaction") by BI Expansion Corp. ("BE"), a wholly owned
subsidiary of CertainTeed Corporation ("CertainTeed").

          The terms of the tender offer and acquisition are to be
set forth in an Amended and Restated Agreement and Plan of Merger
by and among Bird, CertainTeed and BE (the "Agreement").  
Subject to the terms and conditions in the Agreement, in the
tender offer, each issued and outstanding share of Common Stock
validly tendered and not withdrawn will be purchased by BE for
cash consideration, without interest, of $7.50 net to the seller,
and in the event the acquisition is consummated, each issued and
outstanding share of Common Stock shall be converted into the
right to receive cash, without interest, in the amount of $7.50
net to the seller.

          Dillon, Read & Co. Inc. ("Dillon Read") has acted as
financial advisor to Bird in connection with the Transaction.  At
the request of Bird, we acted as agent in soliciting offers for
the purchase of Bird.  Dillon Read has previously performed
investment banking services for Bird, for which we received
compensation customary for such services.  For services we per-
formed in connection with the Transaction (including the ren-
dering of this opinion), Dillon Read will receive a fee upon 
closing of the Transaction.

          In arriving at our opinion, we have reviewed a draft of
the Agreement and certain business and financial information
relating to Bird and its subsidiaries, including audited con-
solidated financial statements, unaudited business segment

 
financial information, certain financial projections, estimates
and analyses provided to us by Bird management, and have reviewed
and discussed the businesses and prospects of Bird and its
subsidiaries with representatives of Bird management and have
compared that information to similar data for other publicly-held
companies in lines of business generally comparable to that of
Bird.  We have also considered the trading history of the Common
Stock.

     In arriving at our opinion, we have also considered the
financial terms of certain other mergers and acquisitions which
we believe to be generally comparable to the Transaction and have
considered such other information, financial studies and
analyses, and financial, economic and market criteria as we
deemed relevant.

          In connection with our review, we have not indepen-
dently verified any of the foregoing information and have, at
your direction, relied on its being complete and accurate in all
material respects.  We have not made an independent evaluation or
appraisal of any assets of liabilities (contingent or otherwise)
of Bird or any of its subsidiaries.  With respect to the
financial projections, estimates and analyses provided to us by
Bird, we have assumed, at your direction, that such information
was reasonably prepared on bases reflecting the best currently
available estimates and judgments of management of Bird as to its
future financial performance.  Our opinion is based on economic,
monetary and market conditions existing on the date hereof and
the information made available to us through the date hereof.

          In rendering this opinion, we are not making any rec-
ommendation regarding whether or not it is advisable for Share-
holders to vote in favor of the Transaction.

          Based upon and subject to the foregoing, we are of the
opinion, as of the date hereof, that the consideration to be
received by the Shareholders pursuant to the Transaction is fair,
from a financial point of view, to the Shareholders.

                              Very truly yours,



                              Dillon, Read & Co. Inc.